Comment by keyringlight

The only thing I'd add is that if you can opt to say "yes" later, it should be obvious where to find it (eg. make a logical settings menu) or they point you to where you can find it. If they really want to make you feel comfortable using their app/site/service there shouldn't be any loss aversion instinct stirred up by hitting "no" as though it's your only chance to accept what they're offering.