If you have friends staying with you, a lock off can provide them privacy. They enter and exit through their own door instead of the one you use.
But if you have a larger family and need the space for your children, a dedicated will provide just the extra sleeping space and no extra exit out of the second bedroom portion. So you don't have to worry about the kids escaping during the night out of their bedroom.
The lock off will have its own kitchenette. The dedicated won't.
The dedicated will have a good chance at having two queen beds vs a lockoff which will always have one queen bed and one double sleeper sofa (except for OKW which always has two queen beds in the second bedroom AND BWV which has no dedicated two bedrooms AND BCV which only has 25 dedicated two bedrooms with two queen beds - the rest have the bed/sleeper sofa set up).
At OKW, the dedicated two bedroom has an extra closet in the second bedroom, plus a second bathroom sink where the kitchenette would be.
Lockoffs will have two balconies. Dedicated might only have one.