why use *?

i wonder why people often use * sign when they want to say something that we already know what he/she want to say it?
like use f**k when they want to say fuck or b*tch when they want to say bitch?
oh come on, when you want to say it, just say it! don't make it look ridiculous by use that. but if you want to say it but you want to look innocent by using *, just replace the word by something else.

no offense, just say what's in mind.