When to compile regex?

[David Shochat]

In section 4.2.3 of the Python Library Reference (1.5.2) it says that
using compile is more efficient "when the expresion will be used several
times in a single program". I'm trying to figure out the intended
meaning of this. Does that mean "executed more than once", or "occurs
more than once in the program text"? Specifically, if it only occurs
once, but that is in a loop, is there an advantage to compiling before
entering the loop?
-- David