I used to think that too. Switches however are simpler and more concrete than "vars", which are just a cheap hack using another unit's death counter or some other number storage (score, resources, etc.), frankly. 99% of the applications for triggers dont require intensive triggers, unless your like me and make even a damn banning feature 10x more complicated than it needs to be, so switches are probably more than adequate. But they can also be a hassle too, like if you need to mark each level in a bound/rpg/def/whatever map where a var could be as simple as "add 1" or "set to #" to mark each level. Plus, switches use up string slots, which may be a no-no in big rpgs where your already groaning under the weight of in-game strings and need every last bit you can afford. But if you just want to mark something that has occured, toggle a background event, or block some set of events from happening, then switches work well.
Over-abrieviated Moral: If it gets complicated, use vars. For simple stuff, use switches.