I wasn't playing favorites actually. I had asked a very similar question shortly before you, and tye had corrected my assertion that perl wasn't comparing them numerically without 0+.
in reply to Re^4: Sorting Puzzle (just sort)
in thread Sorting Puzzle
His statement was technically correct that 0+ was not neccesary to force numeric comparison, as perl already did that. What 0+ accomplished was to force bigint's involvement. A minor, but valid point.
As for reasons to avoid its use I'd guess the hidden cost of the bigint magic, and less than obvious cases where that magic doesn't come into play - such as in the original question.