Is a small memory footprint better for a php script?

Hey,

I'm wondering something about memory usage.
I just looked at how much memory the newest phpbb is using and that's
over 2 mega bytes!!

Now i'm working on a php script that is currently using around 600 kilo bytes.

The question now is: what is better? a script with a small memory
usage? or is that something i don't need to look at?

And when is memory usage gonna be a issue? is that when you have ALOT
of simultaneous users? (lets say 100 all the time.. not that i have
that.. but just for the idea).

Thanx,
Mark.
.