I would also recommend against using both. IMAP is really the best way to go. All devices and clients will be sync with each other and will be able to know what actions have been taken on an email. For example, with IMAP, if I reply to an email on my desktop client and then pull up my email on my iPhone, I will see that the email has been replied to. If I was using POP, the iPhone will not show me that I replied to the email.
Also, another thing to consider is the with the POP protocol, you can only download email from the Inbox. That means that if you set up folders in your desktop client and copy email to those folders, you will not be able to see that email on another device. With IMAP, any folders you create are created on the server and mail moved to those folders is also on the server. Thus, if you view your mail from any client, you still see those folders/email. If you are concerned about not being able to get access to your email if the Internet/server goes down, most email clients have a setting to allow email to be stored locally for off-line use. In some respects, the iPhone/iPad have this function already turned on to an extent.