Why not delete bounced emails?
The main reason to not delete bounced emails from your list is because this prevents you from prospecting them again. Bounced emails don't count against your lead credits or emails per day.
There is no harm in trying to contact a lead with a bounced email address. There are cases of email servers being down and offline, and keeping the bounced lead on the list could lead to an opened email.
However, if you would like to stop emails to the bounced leads you can mark them manually as "Unsubscribed". To edit the status of a lead click here.