Size of varchar

If I have a varchar that the developers are not sure how large it will be -- they guess 50-100 chars but may grow later -- and is not going to be indexed -- is there any reason *not* to create it as a varchar(255)? From all I can read there is no more overhead or space taken with a varchar(255) where all data are less then 100 chars than defining it as a varchar(100). Am I overlooking something? TIA, Tom Grenier DBA, Biztravel.com