I agree that if you don't play to go to that casino for a long time, you shouldn't leave any amount because it might be hard to withdraw when you comeback and they'll ask you to comply with some requirements that you have to. I've got several casinos registered with my email and gladly, I'm receiving promos and other notifications that seems to be important to me because it's hard to maintain being active in all of them.
Yeah, it's true and there is always an option to opt-out of the notifications and emails from a particular casino if you want to do that, by clicking the unsubscribe button at the bottom of every email. I think email is the best way of getting promotional offers because you cannot visit a casino daily to see if there is a new bonus for you.
While notifications on the site are good when you are active on the site. For example, when I reach a particular VIP level on a casino they would not email me because they know I am aware of it and have seen the on-site notification.
Maybe some casinos send one too many emails which leads to the players banning emails from them. Casinos need to make sure they do not send emails for every little thing and if there is something a player is interested in, then only send those emails.