I'm of the same mind as Neonivek regarding Source Spells. Of course this is on Classic difficulty and is yet to be seen on Tactician where Source Spells might become mandatory for certain fights, and is my personal opinion.

Having completed the first act over 10 times, completing everything there is to do every run, I realized I NEVER use Source spells. The only times I remember it's a mechanic is when it's needed to open a door, activate a shrine or when I see a source spot on the ground, but then forget about it immediately after.

While the lore behind it and concept are cool in theory, being limited use (even though you can get 5+ from natural sources and 16+ from source vampirism) means you keep them for the next boss fight you can't win without. But since that never happens, you finish the act without even memorizing a single one of them, keeping the wand/helmet charges and source points for the eventual future acts where it might become needed (Which I doubt considering how the first act has panned out, and even if such an encounter should come, there are so many source points available that I doubt using a few/all of them in act 1 would become a problem). Therefor making us never use Source spells ever.

I feel like they are only used by people who either force themselves to use them because they know they will have plenty of source points to spare later, or people who somehow get into a situation where they can't win the fight without pulling out a trump card in the form of an overpowered spell to turn the situation around.

You can compare this mechanic to having a 1 time use unique item at level 1 that instantly kills an enemy when used. You would carry it until the end of the game because you didn't want to waste it on anything but the final boss, which you still wouldn't use on because you'd want to experience the final battle like it was intended. Of course this is different because you can recharge the spells and they aren't instant wins, but the feeling of waste is kept because of the limited "charges" mechanic.

TLDR. You never need to use Source Spells, and it feels like a complete waste if you ever did.