Though i cannot say when to use call, all that i can say from my vb programming is there is a subtle difference between

SomeFunc someinput

and

Call SomeFunc(someinput)

Specially when you write functions/subs which take object or control pointers, because without the explicit Call and ( ), VB sometimes replaces it with default value or property, and sometimes (in not so well written codes) can give problems/unexpected behaviours.

RK