FAQ/Slowed performance - tools and connections

From VFXPedia

There is a known issue with the Hierarchy and Reverse settings in Timeline View causing slowdowns on large comps, as it has to sort out the tool tree and connections. Setting this to All Tools will restore the speed of the comp.

Versions prior to Fusion 5.1 may also experience slowdowns when making or breaking tool connections in large comps with many interlinked branches. These delays have been eliminated for 5.1 and later.