I have heard it said that sometimes therapists will take on only one or two "difficult" patients at a time. By which I mean people who are very needy, need a lot of contact, etc. I would imagine that therapists need a good blend of patient types. If a therapist only has borderline patients, they're going to get overwhelmed and burned out from the constant needs of contact and reassurance. If they only work with people with "slight" problems, they might feel like they're not doing the most good. The most difficult patients have the potential to recover the most, but you can't have a full caseload of them - you'll go nuts yourself. So, yeah. I'm betting most T's like to have a blend.