Suspending a hold lets you continue moving up a title's wait list without the title becoming available to you. If you reach first place on the wait list, you'll be in the first position to get the book when your suspended hold period ends.
For example, you might want to suspend a hold for a popular eBook if you are getting close to first in line but are currently reading another book.
You can suspend your holds in your eBook record in OverDrive (instructions).