I'll prolly send everyone I can away in one playthrough or another (like when I try to solo the game as a challenge to myself).
As for getting rid of certain companions and why, well, it depends entirely on the context. Let's say I'm playing a Templar Radicalist Inquisitor who firmly believes all mages should be gutted, or at the very least get the brand. I doubt Solas, or Viv, or really even Cassandra would be non-too-tickled by that notion. The context behind a characters creation and the characters personalities, wants, desires, and ambitions is what will set the tone for who and who does not get into the Inquisition.
A good example of this is in DA:O. I played a Mage who loathed apostates, or blood magic, or pretty much anything Anti-chantry. I dropped Morrigan like a bad habit, left Sten to rot, and formed a proper group of Pro-Circle/Chantry in the order of Alistair, Wynne, and Leliana. Zevran I let live, but he was camp bound and eventually betrayed me. Shale I let live but can't really remember if I gave any indication I believed she deserved her freedom (think I did, but whatever). And Oghren... well, every Hero needs his dwarf, I just made sure to keep him downwind and specced him into Templar so he'd be a closet Andrastian (head canon, huzzah).
Anyway, I suppose the point is context. Need to have it, and until we learn these companions stories, I can't really say yea of nay. But I can say strudel.