The strings generated by password managers are often incompatible with arbitrary requirements imposed by websites. You must use a symbol, but some symbols are forbidden and we're not going to tell you which ones! You can't have more than N consecutive numbers! Your password is too long! It must be exactly 15 characters long! etc. etc.

So I restrict my password manager to use what I consider to be a widely accepted subset of the printable characters, and then some random website will complain about the lack of this or that character. :(