Toontrack is the only music software company that I have seen impose a limit like this. This limit does nothing to reduce piracy or oversharing of licenses beyond what the concurrent installation limit already does.
I own two computers. I have Superior Drummer installed on both. I like to reformat my hard drives about once a year in order to cut down on unnecessary bloat. Doing this once means that I have now reached my activation limit. To do this again next year I will have to e-mail Toontrack and ask them to reset my activation limit AFTER removing the licenses that are currently being used (meaning it is impossible to have a period of no downtime). There is also no guarantee that my request will be granted, so I could just lose my ability to use the software I paid for permanently.
As long as this ridiculous limitation is in place, I will no longer be purchasing any Toontrack products. The mainstream alternatives, Addictive Drums and Steven Slate Drums, both have more sane activation policies and I will sooner switch over to one of them than buy an upgrades or expansion packs for Superior.