It's a bad idea for a public forum, that's for sure. But a good idea for a private forum used for business / projects in software development. Keeps people in the loop of new threads and new posts therein. Emails won't go bad because if an employee drops, their forum account is inactive/deleted. Subscription emails don't apply then.
Regardless of all this, my lazy users will stick to Daily Updates for Thread + Post updates

Choosing "Instant" with this plugin is only for threads and that is not good enough for them.
-D