I've posted quite a few times about competitions from various perspectives, but I think a lot of people get too hung up on all training being solely about competition (and sometimes even specifically IBJJF rules). I look at jiu-jitsu as much more...
It includes sporting competition for sure... gi and nogi grappling competitions under various rulesets... but also MMA & vale tudo. The most important thing about jiu-jitsu is that it gets tested. Doing that in training is one thing, but doing it in competition helps you develop in different ways. Testing yourself in whatever form of competition you want to is definitely something I think everyone should do.
Beyond competition, it's also a martial art which should give people skills they can use in a real life fight... physical and mental skills. Training jiu-jitsu gives you techniques and the ability to perform them on fully resisting opponents, that's always the case. But it should be teaching you to do that in a tough environment, there should always be lots of high intensity sparring. That level of intensity also improves mental toughness... you get used to dealing with being in terrible positions, unable to move with tons of pressure on you. Toughness is another aspect which effects a fight... along with technique, strength, size, cardio, flexibility etc.
Then it's also a hobby (activity?? hobby doesn't seem to do it justice) or even a way of life as some people describe it. The vast majority of jiu-jitsu you do is going to be in training, so really your only things to consider when rolling are to not get injured and not to injure anyone else... it doesn't matter if you leg reap someone in training, just don't smash your leg into it and twist your partner's knee. It doesn't matter if you grip inside the trouser leg either, or use a wrist lock on a white belt. Just do your best to not hurt people.
So yeah, competition is a massive part of jiu-jitsu, but I see competition as a place to test your jiu-jitsu skills not solely the aim of training. Now, if some people want to train just for competition, that's cool with me too, but I think they're missing out.