in reply to
Parameter validation for numeric function arguments?
The origin of perl was as a sysadmin tool, and in other situations where people frequently wanted results quickly, and might tolerate a few aberrations if they got the bulk of the results.
If you want to run a nuclear power plant, or a 747, definitely, validate your inputs.
If your boss wants you to extract some information from the web logs to see how soon the current heavy load will bring down the web site, take advantage of the fact that '123xyz' in a numeric context is treated as the number 123.
As Occam said: Entia non sunt multiplicanda praeter necessitatem.