There were many reasons for the Yankees to spend $180 million on first baseman Mark Teixeira on Tuesday.1. In my column in today's Post, I wrote about how similar this offseason was for the Yanks compared to the 2004-05 offseason. That year they decided not to sign Carlos Beltran, a switch-hitter and top defender repped by Scott Boras. This time they decided to spend the dough on Teixeira, a switch-hitter and top defender repped by Boras. Just check out the upcoming free-agent markets. They were not going to be deep in prime-aged positional standouts. So if the Yanks did not act on Teixeira now they were going to regret it in the near future.2. Don't ignore age as a factor in this. Teixeira turns 29 in April. Last year, the Yanks spent too much of the season depending on the too inexperienced and the too old. But since the start of last year, they have added Xavier Nady, who will play next season at 30; Nick Swisher, who will play next season at 28; CC Sabathia, who turns 28 in July; and A.J. Burnett, who turns 32 in two weeks.This gives them significantly more players in their prime, and should be of great benefit if Robinson Cano , 26, bounces back from a poor season; Chien-Ming Wang , 29 in March, returns to 19-win health; and Joba Chamberlain , 23, can avoid the disabled list.The Yanks suddenly have a lot more players who could be considered near or in their prime.3. Don't ignore the defense. Teixeira is probably the second best offensive first baseman in the majors after Albert Pujols. But he probably has no rival defensively. The Yanks have been abysmal in recent years in the field, particularly at first base. Now with Teixeira at first, either Nady or Swisher in right rather than Bobby Abreu and perhaps Brett Gardner in center, their range should improve markedly.4. It can't be ignored that the Yanks kept Teixeira away from the Red Sox. He helps the Yanks, no doubt, but this also hurts Boston.5. I fully suspect that the Yanks are going to make a trade or two now. Teixeira's presence allows them to make the best deal available for at least one player from the group of Johnny Damon , Hideki Matsui , Nady and Swisher.Damon, Matsui and Nady are all free agents after the season, and all but Nady have no-trade protection. My suspicion is that the Yanks would want to retain Damon the most for 2009 because of his leadoff skills. All things being equal they would move Matsui since they are trying to improve on defense, and he provides the worst fielding option of this quartet.The Angels (who failed to sign Teixeira), Rangers , A's and Rays are all in the market for more hitting. The problem for the Yanks is that the free-agent market has a glut of hitters such as Milton Bradley, Jason Giambi , Pat Burrell and Ken Griffey available. So making a trade will not be easy.The Yanks have some surplus set-up relief to spice up a trade and I do not think it is inconceivable that they could try to do a huge trade that would include Wang, who is two years from free agency. The Yanks would have to know for sure that Andy Pettitte is returning plus, possibly, know that they could get another starter they like.If they are able to find trades, I think they should concentrate on trying to add two elements: 1) Multi-dimensional players. The Yanks have a wonderful looking starting lineup, but their depth is still hardly inspiring. So they can use a few do-everything kind of guys such as the Angels' Chone Figgins or the Braves' Martin Prado to rest regulars and provide insurance against injuries. 2) The Yanks should emphasize positional prospects. They are really lacking in that area in the upper reaches of their system. For example, the Braves have had a tough time completing deals this winter. They have liked both Nady and Swisher in the past; in fact they tried to obtain Swisher this winter before the Yanks did. Atlanta has three well-regarded minor league center fielders in Jason Heyward, Jordan Schafer and Gorkys Hernandez. Could the Yanks turn a regular outfielder into one of those prospects?6. Don't ignore that Teixeira is a switch-hitter, who brings power and patience to both sides. The Yanks also added another switch-hitter, Swisher, this offseason to join Jorge Posada. During the recent dynasty, the Yanks enjoyed the strategy-destroying element of having elite switch-hitters such as Posada, Bernie Williams, Tim Raines and Chili Davis.7. Don't ignore that Teixeira is a legit No. 3 hitter. Who was going to hit there for the Yanks without him? Matsui? Cano? Jeter dropping down from the No. 2 hole? A-Rod moving up from cleanup?8. Hey, it is tough to be the Mets right now. Sure, they solidified their end of game relief with Francisco Rodriguez and J.J. Putz. But these electric additions by the Yanks have clearly kept the Mets as the second team in town in an even stronger way, at a time when they are opening a new stadium, too, and also have their own TV network.And it is hard to ignore that Met owner Fred Wilpon lost an exorbitant amount in Bernie Madoff's Ponzi scheme and the Mets' new stadium is named after a financially troubled bank. The Mets might not have the dough necessary to fire back and create a greater excitement around the team.9. Without Teixeira, the Yankee lineup might have been good enough, especially if Jorge Posada and Hideki Matsui bounced back from injury, and Robinson Cano honored his skills fully. But if that didn't happen and/or there were injuries again, the Yanks were once more going to take a significant nosedive in offensive talent. Teixeira makes them more bulletproof to an offensive snooze.He also should make it easier - if the Yanks decide to go this way - to emphasize defense in center with either Melky Cabrera or Brett Gardner.10. Manny Ramirez never made sense for the Yankees. He is one of the great hitters ever. But he was another guy who was going to hurt their defense. He was going to be another guy well beyond prime age. He was going to be someone who would challenge authority at a time when manager Joe Girardi does not have a firm hold on the clubhouse. Teixeira conversely is a disciplined kid from a military family who will not have trouble with Girardi's no sweets in the clubhouse edicts.