Well, if your intent is to not delete from the server, then you should be using "hide". When it's set as the default for an account (which sounds like you've already done), the app's lower left delete icon will change to reflect that.
The logic of "Delete now" and "Move to deleted" message deleting methods won't be affected by your choosing "hide" as the default.
They'll continue to delete messages from the serer, and will continue to be available in message lists, just not as an icon, but in the menu.
The logic behind this is that one message deleting method is chosen as the default and easily accessible via an icon, but the other two can still be used, for flexibility.
