I pretty much always use my starter. In fact, if I don't, I feel really weird. Same thing with having a Flyer. I need a bird Pokemon on my team, and I need a Starter on my team. At the very least, I need a Starter-esque Pokemon (Cubone, Sewaddle, Porygon, Tympole, and other Pokemon) to use as my Starter.
They're sort of like team leaders, and additionally, they're the first Pokemon you emotionally connect with (if you do that sort of thing (which I do)). So for me, a team without a Starter is just a group of six Pokemon. There's a strange feeling of synergy that is present when a Starter is on your team, in my experience.
So, I always raise my starters and keep them in my team.
It helps that I love almost all of the Starters. I really love all three Unova Starters, as well as Turtwig, Totodile and Cyndaquil, Bulbasaur, and all three Hoenn Starters. If I were to simply construct a team out of thin air, it'd likely include a Starter from some region anyway.