lets not forget that on alot of our mopeds they are well over 20 years old, and the metal filters that are supposed be there are not. now replacing a petcock valve would solve that, or a banjo, etc. but there are many people here that can't,or won't go for the $$ of a new petcock, etc.
the next best/cheapest thing to do to fix that is a $2.00 fuel filter.
peace of mind in my book, and like don-o said, they last many, many miles.