But I didn't like it much and I am currently playing a mini_my_version_of_BiG BGT game without the modification.
Reason attributed too:
1. As your character levels up, you don't actually need the mod because you have quite a number of spell slots (directly due to character levels or indirectly).
2. Reduces gameplay interactions/features,
--like many spells redundant (as you'll never ever use them. As you get access to high level spells..you'd mostly use them and wait for the cooldown, rather than use low level spells)
--makes repeated, but fun part of identifying items redundant (as you can have one slot of identity spells and keep spamming it)
--spamming heals (making you not to utilize healing potions or other characters to have healing ability)
--having limited spell slots pushes one to think what would be the best combination of spells to have for either prepared or unprepared scenarios (else you'd just have one or two spells and keep spamming away the same thing every time)
3. Spell casters are already powerful in the first place after a few Character levels, with this modification you'd be outright breaking the game out of its socks, nickers and whatnot in BG2; when you have access to some mind blowing array of powerful spells and casting it over and over, again and again. <- can really turn out to be boring with the mod
4. You anyways need to rest
--To rejuvenate from fatigue..
--Trigger some In-Game events (Dream sequences in BG1 and BG2)