OOOH, that's a neat idea!I use it for sorcerers only,
That's a bad thing because ... why?Whatever you do, don't ever use it for the Warlock. According to the DMG, the Universe will legit imploded if done.
And then your Patron's credit card get declined when they go to Red Lobster for dinner.
Cuz then your Warlock doesn't get any of those delicious cheese bisquit things they have.That's a bad thing because ... why?
The big issue is using it outside of the 6-8 encounters per day. This lets a character "nova" every combat, since they just don't care about low level spells. With extended encounters, they will have to fall back on cantrips much quicker if they do this.I've always wanted to try them.... but in the end my players weren't interested in the extra bit of math.
I think they give you more flexibility, but may change the balance of encounters if the players jus send 5th level spell after 5th level spell all day.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.