It may be just "cargo cult".

perlsub says "most" routines would do it, but you don't "have" to.

from perlsub:

 Most AUTOLOAD routines will load in a definition for
 the subroutine in question using eval, and then execute
 that subroutine using a special form of ``goto'' that
 erases the stack frame of the AUTOLOAD routine without a
 trace.
[download]

note: I did think it was a performance issue - it is not.