I have noticed a huge performance hit when number of Resources/Groups increases.
I'm using Scheduler 7.7.3078.1.
I load it with 200 resources in 25 groups more or less equal in size.
The more groups I expand the slower it gets to expand following groups.
Sometimes it takes up to few seconds.
Debugging UI Responsivnes with IE I can see a LOT of events firing as on the attached screenshot.