On mobile you usually just stay logged on for email accounts. I always have no matter what mobile OS.
If you are getting too many notifications, you can either change the sync frequency or turn off some/all of the alert methods.
Settings > email + accounts > tap the account name > change the "Download new email" setting... manual might be best if it is a seldom used account...
Then you can sync from inside the email box or Settings > email + accounts > hold down on the account name > tap "sync" from the popup menu...
To change how alerts are handled... Settings > notifications + actions > tap the account name > change conditions to make it less intrusive.
The last resort is to go to email + accounts > hold down on the account name and tap "delete"... But it would be silly to delete the account after every use...
There are a few reasons mobile stays connected to email accounts:
- Your phone is a comm device - a smart phone is a hub for all your comm, of which email is a part
- Usually there are other account benefits aside from email, your phone stays connected to leverage those account benefits and services
- Syncing your email account can also update your contacts and calendar as well, so they remain current on your phone without tedious replication of entry