Mana management is a part of the healer job, and when we heal and dps, we know how far we can go.

I hope you don't base your idea on people who are doing this in the wrong way.

When we are two healers in a static, we know who does what at which moment so that we don't burn all our MP together.

If you are in df or pf, since you don't know with who you are playing, you might not play the same way.
Always need to adapt.