Very necessary.

As senders, we have to verify first the addresses that we'll be sending our funds. Because if we're not going to do it, it's likely that an address that's kept in our records are no longer in use.

We don't know if the receivers like to delete records of theirs that includes wallets but I don't think it with the exchanges. Just verify and always do it, it will always save us from too much trouble.

It will not take a lot of time to ask first if the address is still in use or possession of the receiver although it's never gone to them as long as they have access to it.