Even if you barely pvm (like me) you still get through overloads fairly quickly. I made 2.5k of them over the course of 99 herblore, and have just over 1k left. The only time I use them is for slaying, dungeoneering and very occasionally for PvM. That said, I definitely wouldn't lamp herblore.

 

If you don't have the charms banked, lamp summoning. If you do, lamp slayer unless you don't care about xp post 99. In which case do agility.

Except Kiln & QBD, which are both over 5m/hr and that makes them the best gp/hr in the game outside merchanting. And you need overloads for dungeoneering as well.

Ya, there are definitely some uses for them, but it's not a good idea to make several thousand.