Makes sense, what are the most typical purposes of special assessments?
SAs are for any unbudgeted item(s) that the HOA Board feels is necessary. I've seen them assessed for everything from renovations to ADA/health code compliance to covering shoddy workmanship.
Because they are met with such controversy, most of the hotel-branded TSs simply build healthy reserve funds into their annual MFs in order to avoid SAs for predictable events, such as refurbishments.
As far as Starwood goes, there are only two that I can recall:
Back in '08, SVR imposed an SA for ~$1500 per week (varied by unit size and regime), payable over 3 years, in order to do a major refurbishment.
Back in '07 (?), WSJ Virgin Grand aka Hillside tried to impose SAs for renovations but lacked the votes necessary. I think they eventually were able to pass a pared down SA but I'm sure WSJ owners will remember better than I do.
Since then, all resorts have raised MFs in order to build a capital reserve fund so that they (theoretically) won't need to impose another SA for renovations. Things like natural disasters and shoddy workmanship are still impossible to budget for.