Need vs want...

It's an age old debate, I know, but that doesn't stop me from adding my views!
I got thinking about it today after a good friend advised me against trying to help someone because I didn't need the extra hassle....
She's probably right - she usually is, annoyingly, but that won't stop me doing it.
It's something I've been discussing with my therapist in our last few sessions, and disagreeing with her about too.
Unfortunately (or fortunately!) I'm one of those people with a very active self-sacrifice schema (see here if you're baffled already... http://www.schematherapy.com/id30.htm) which means I have a bit of an over-developed need to help people.
I have real trouble seeing that as a bad thing, and when I voiced that to my lovely therapist, she said it wasn't necessarily a negative unless my desire to help others impacted on me.
Which would seem simple enough, but I think that is where the problem lies. I genuinely have difficulties accepting that whatever I want or think I need at any one point in time can be more important than someone who genuinely needs my help (note to colleagues - I am aware of this difficulty so that doesn't mean I'll do all your work for you!).
For example, a few of my friends have or are about to have their second child. And as I can remember so clearly how soul-destroyingly awful life with one newborn was, and can imagine how difficult it must be when you add in a toddler as well, I am ready and willing to help however I can. Even if that means going off on a rescue mission when I'd like a quiet afternoon at home.
Is that wrong? I would say that if I'm doing it cos it makes me feel good or needed, which I'm not, then it would be a bad thing. But I think I'm doing it because I don't want others to have the kind of endless, bleak, excruciating hours and days I had when Tash was tiny.
Maybe there's an implication there that I wanted someone to do the same for me. I think there's some truth in that. And while people were as supportive as they could be, with the knowledge they had at the time, there is probably a lot more they could have done. But just because they didn't, does that mean I shouldn't? Surely if you believe in karma, or any kind of "do as you would be done by" philosophy, you would want to help in the hope that should you need something in the future those same friends would stand ready to help?
There can be a bit of a difficulty there though - if those friends don't have the same self-sacrifice schema going on there's a risk they may genuinely want to help but feel that time with their children, husband or at work is more important.
I'm still not sure how to find a way through all this, but for the moment I'll keep going with my rescue missions and building up those brownie points. If it's not hurting anyone but possibly me then I think it's worth doing.