If your bike experiences a lot of water especially that of the salty kind you might want to clean and reapply more often but if you generally take care of your bike and it doesn't see much water, you probably don't need to worry much. I wouldn't personally worry a lot about it as people have said most don't apply or haven't done so in a while and their bikes are OK.

I don't think it is harmful to the bike and isn't a bad thing to do once and a while but mostly for the disassembly of the bike so you can clean and re-grease things and check everything once and a while.