Like you, Gabi, I usually let the Elite 4 lineup decide what I have on my main team. So while going to the gyms and through the storyline, I train six Pokemon plus a few promising extras. The problem with training usually comes after the Elite 4, when I like to catch Pokemon on a low level and train them up for other purposes. As you can guess, training them at that time is difficult because you usually don't have the trainers and gym leaders you had earlier on. When some games had the gym leader rematches, they were of too high of a level. But I guess that's what Exp. Share is for, but that means I still have to use my main team!

Plus at the start, even though I do have the Elite 4 decide my final lineup, there are some guidelines on what to bring along. A Water type is a must, as well as a Flying, Fighting, and Electric type. I've learned the necessity of a Steel type to train for fighting Dragon types even though they have the possibility of knowing Earthquake. For some reason (probably because it takes a while to catch one), I've never had a Dragon type for the Elite 4.