Regarding Kodi's legality, it depends. Like others have pointed out, it can be used to "steal" content, such as PPV UFC fights, movies, tv etc, but that part is still a gray area. It is undoubtedly illegal to be the provider, but the consumers are so far untouched. There have been rumblings in the U.K. from internet service providers, but the worst anyone have seen is their internet speed throttled. VPN services is a good way around that for those worried.
There are however many other uses for Kodi, such as streaming free content, or content you pay for, to devices not able to receive a normal signal. 
Another area could be streaming content not available to subscribe to in your current area. As an example, I don't have any way to subscribe to and pay for Racing UK (English horse racing channel), TSN, Eurosport, etc. if I could I would. I stream these without a second thought.
I also stream content from the BBC, which they provide for free on their website, on YouTube and other means, but I don't want to watch on my computer. (They have a ton of documentaries). I usually stream the olympics, because I think NBC's coverage is horrific, but they also have it all online, untouched for free if you have a cable subscription.
 

  as with everything it can be abused, but just because it is possible to abuse doesn't mean that is the only use. K4 mentioned wanting to see PBS, that is free, and if OTA isn't possible, Kodi can be an option.
ETA: stupid autocorrect
ETA2: I am watching a documentary on the Bradford City stadium fire right now. No way that is ever making it to any US channel, but BT Sports stream it for free.