Yes there is a difference. Both CR-1s and SWU's go into "reserve" status as soon as you request the upgrade even if you are waitlisted for all segments. When they are in reserve you cannot use them to upgrade other flights. With e500's there is no reserve status and they are only deducted from your account after you checkin and pay for the upgrade.

There is no need for e500's to go in reserve because, unlike CR1's and SWU's, e500's can be purchased. So if you overextend yourself and upgrade more flights than you have e500's to cover you can just purchase more at the airport if needed.