Outlook creates offline copies of your mails thus letting you access emails even at the absence of internet. Thus Outlook is helpful. Moreover, you can use POP server to permanently move your emails from the mail server to your system thus saving space on the server.
Outlook can be corruptive at times, thus, have Outlook Mac Database recovery tool by Gladwev for recovering the corrupted emails. for reference: http://www.gladwevsoftware.com/olk14-message-recovery-on-mac/