How often do people use \A and \z (match start and end of a string)
instead of ^ and $ (match start and end of a line within a string)?

This question is prompted by:

(1) part of a post in the "What are your ruby rough cuts ?" thread:
  * Regexp ^ and $ work match more than just start and end of string.
  For example, /^abc$/ does not match only "abc" but also "rm -rf /*\nabc"

Comment: using \A and \z seems to avoid the unwanted(?) matches.
Am I missing something?

(2) a Regexp used in the Find module
    if File::ALT_SEPARATOR and file =~ /^(?:[\/\\]|[A-Za-z]:[\/\\]?)$/ then
  which matches "start of a line" + X + "end of a line",
  where X is one of   /   \\   C:   C:/   C:\\

Comment: using ^ and $ in Find will match in the (admittedly rather
unlikely) situation of a file path string containing "\n/\n", and I'm
wondering why ^ and $ are used in this Find module regexp instead of
using \A and \z.