On a game-by-game basis...
Owning a QB/WR combo from the same team will increase your variance (i.e. more likely to boom, more likely to bust) compared to a comparably ranked QB/WR pair from different teams.
Owning a QB/RB or WR/RB combo from the same team will decrease your variance (i.e. less likely to boom, less likely to bust) compared to a comparably ranked QB/RB or WR/RB pair from different teams.
It then stands to reason that a QB/WR/WR combo would be even *MORE* volatile (huge boom chance, huge bust risk), while a QB/RB/WR or RB/WR/WR trio from the same team would be pretty comparable to a similarly ranked trio from different teams.On a season-by-season basis...
I haven't seen any studies on the subject, but I suspect that grabbing any combination of players from the same team, regardless of position, would increase your chances of *ALL* players outperforming projections, as well as your chances of *ALL* players underperforming their projections.
I suppose it's also possible that, if you grabbed a QB/RB combo, if the QB underperformed the RB would be more likely to outperform... but personally, I don't think so. It seems to me that improvements in the passing game more often than not correspond to improvements in the running game, and vice versa.Given this information, we can draw the following conclusions:
Starting a QB/WR pair from the same team increases your chances of finishing the week with the best score, and also increases your chances of finishing the week with the worst score (compared to starting a comparably ranked QB and comparably ranked WR from different teams). As such, this strategy favors leagues that offer some sort of reward for finishing with the best weekly score (whether cash or a tiebreaker), and is a hindrance in leagues that penalize having the worst weekly score (such as survivor leagues).
Starting a QB/RB or RB/WR pair decreases your chances of finishing the week with the worst score, but it also decreases your chances of finishing the week with the best score. As such, this strategy favors leagues that penalize bad performances (such as survivor leagues), but is less valuable in leagues that reward good performances (such as those with cash payouts to the top team).
Variance always favors the underdog, so a QB/WR combo from the same team is more advantageous if you have the worse team, while a QB/RB or RB/WR combo is more advantageous if you have the better team. This applies both to head-to-head as well as to all-play (if your team is in the top half of the league, look to minimize variance).
Over the course of an entire season, starting a QB/RB/WR trio or a QB/WR/WR trio or a RB/WR/WR trio (or even a QB/RB/WR/WR/TE quintet) will increase your variance, which increases your chances of finishing the season with the best team in the league, as well as your chances of finishing with the worst team. Since there's often no advantage to finishing 6th instead of 12th, but there's ALWAYS an advantage to finishing 1st instead of 6th, I would think that loading up on players from a single team would be a winning fantasy football strategy.Of course, it's very important to mention that variance is a very minor consideration, and only comes into play when looking at comparably ranked pairs of players. For instance, you should always start Tom Brady (QB1) and Randy Moss (QB1) over any other possible combination with no regard to variance, because they're higher ranked than anything else you could throw out there. It's only when making a comparison such as Peyton Manning (QB3) and Reggie Wayne (WR6) vs. Drew Brees (QB2) and Steve Smith (WR7) that this analysis comes into play. In that case, because both pairs are comparably ranked, they can be considered roughly equivalent when discussing whether you'd rather minimize variance or maximize variance.