Most users today make use of IMAP emails accounts. Although there is nothing wrong with IMAP accounts, your mailboxes can fill up very quickly and impact your web hosting space.
If you have multiple devices including a desktop, and you want to keep control of your email space usage, then you can setup one device as a POP3 to download your emails.
You can setup your desktop as a POP3 and in your email program, set your emails to be removed from the server after x amount of time. 1 or 2 Months might be reasonable. Since you have set your desktop to remove the emails from the server your space will not build up. You will always have all of your email on your desktop as POP3 accounts will download your email.
You can keep an IMAP account on your other devices (for example phone). Your IMAP device will always have the last Month or whatever you set in your email program available as IMAP'S sync with the server.
To learn more about the differences between IMAP and POP3 look here: https://dev2host.com/support/index.php/knowledgebase/2/Difference-between-IMAP-and-POP3.html
Please login to your cPanel and email accounts area to find appropriate settings for your email accounts or open a support ticket if you need help.