Yeah apparently he mentioned other trigger options but originally wasn't sure on how to use them so he just kept using Switches. Hopefully future projects will benefit from this lesson.
IIRC he said he used a lot of Common Events early on that could have been Flags or Switches and needed a workaround to get more CEs. After some Googling I think the issue isn't the game engine itself but the RPGMaker editor. (Code spaghettification probably also factors in.)
Common Events are reusable bits not tied to a specific NPC/event, like sprites wandering, the "quest received" animation, day/night lighting, environmental sounds, etc. Having several things call up the same bit saves on coding and ensures consistency. If CEs were used instead of other things listed below I can easily see them running low even with a workaround.
Flags are coding symbols for maps (tiles, items, sprites, etc.) and don't have a max. Mostly used for defining what spots you can & can't walk into ("collisions").
Variables measure things, capped at 5k editor entries. Collecting boars to complete "Boar Hunt," distance something can spot you at, days since you knocked up a girl, inventory, etc.
Switches activate if the conditions are met, also capped at 5k. Global switches activate anytime the conditions are met though you might need a specific action/event/NPC for the effects to kick in. Self-switches only affect one event like opening a chest or changing the dialogue. Not sure if self-switches count against the 5k limit in MV, but each event in MZ can have up to four self-switches that don't count against the global cap.
- MV's built-in editor has a limit of 1k CEs but can go higher, and a fixed 5k max each Switches & Variables.
- MZ has 2k CEs and can go higher, but still 5k Global Switches & Variables. Tinkerer didn't move to MZ for various reasons when it came out.
- Increasing CEs increases instability with both...