Pausing a hold is a good way to hold your place in line on the waiting list for an item. However, there are a few times when you won't be able to pause a hold:
The item says "check shelf"
You can't pause a hold if the item is currently available.
Even if your hold isn't #1, if there are enough copies available to fill your hold, you won't be able to pause it.
The hold status is "In Transit"
The hold status is "Ready"
For system reasons, you are not able to pause a hold that is more than 255 days old (approximately 8 1/2 months)