disney with wheels

[Tiggerish]

and he still had to transfer out of it to get on pooh and a few other rides

That is exactly right, he can stay in his power chair all the way up to the ride boarding point but not all chairs fit in the wheelchair accessible car. I have a bit smaller chair but it has low ground clearance so pooh and buzz are transfer to a regular car for me also. Little Mermaid, Jungle Cruise, Small World, Great Movie Ride, Toy Story Mania and the boat ride in Mexico, I can stay in my chair.

 

[SueM in MN]

It depends on the size of the wheelchair and also (for some attractions) the total weight of the wheelchair and the person.

My daughter has a Permobil F5 VS. I just measured it and even though it looks huge, it is only 26 inches wide by 40 inches long - that puts it in the 'footprint' for attractions of no more than 32 inches wide and 48 inches long.
Her wheelchair is very narrow - her seat cushion is only 15 inches wide.
According to the wheelchair owner's manual, that model can be up to 31 inches wide, which would be an exceptionally tight fit in some attractions. The owner's manual says it is 191 kg - or 418 pounds (much heavier than I thought ) that includes the batteries, but not accessories, such as the seat.

Some attractions have a weight limit of no more than 800 pounds total, so some users might be too heavy.