It's not good for the longevity of the SSD to constantly write files. In the case of BTT, I expect it to not rewrite the its configuration when I don't change anything on the configuration. However, it seems the file is constantly rewritten, which is not really appreciated.
macOS automatically schedules and handles the writes to these saved defaults. They already optimize this a lot and the same happens for tons of system plists - such plists do not only contain user settings but also app state. (For example the last window positions, statusbar item position etc.). A lot of this is done by system frameworks and can not be influenced by app developers.
I'd recommend apps like FSMonitor if you want to see how the system schedules the writes. https://fsmonitor.com
Thanks for bringing some light to it. I attempted to sync the file across devices and noticed this. I guess then it's wrong to do so. Instead I export and import again, but it's annoying when I do changes. It would be nice if BetterTouchTool could also maintain a file that only features settings and triggers, so that it can be synced properly. But there is more to it, like it would have to watch the file for changes in case two machines are actively running. Collisions could be handled by the sync program (whatever it might be, Syncthing, git, etc.).
I guess that's probably too much to ask, though.