Pass by reference, or return?

[Moonglobe]

when you write functions, do you generally write them to modify the args passed by reference, or return the computed value? obviously sometimes it would only make sense to use one or the other, but where you have a choice, which do you prefer? personally i like returning because it doesnt necessitate use of temporary variables when i want the original value of a variable i pass by reference, but i'm interested in you guys' opinions...

[laserlight]

In PHP I simply prefer to pass by value when only 1 value gets modified, probably because that was one of the first things learnt when working with functions.

In other languages I tend to consider my options more, partially due to efficiency.

[Weedpacket]

I prefer to have the result returned in most cases; consider that you can do $foo = array_unique(array_merge($foo,$bar)); but $foo = sort(array_unique(array_merge($foo,$bar))); won't do the Right Thing.