There are multiplem uses, as you could read in BAS
description. You can experiment yourself and find out
how you can use it.
Typical situation to use it is proxy checker - You can run
such function in 100 threads for example, so all 100 threads
will open at same time and do that proxy check much quicker
than in standard BAS, which would work sequentionally and
open threads one after another and work lot slower to check
1K proxies for example.
But there is another use as you could read in description in
BAS. Its a situation when you have main script, but need a function
that will execute before and after main script finishes.
So basic difference is that call function in several threads works
in paralel, while simple function call works sequentially, one function
after another (NOT in paralel)