A while back, I'd given my players some questionnaires about our campaign to get feedback, requests, complaints, and compliments. That way I could know what's working, what's not working, what people like and dislike, etc.
One of the complaints was the limit of learning one spell per downtime for wizards. I didn't put a limit on clerics, mostly because they have such a limited list and don't actually learn their spells. The Good God grants them, so that doesn't need to take a week (heck, with a good prayer, it's possible to take place instantly . . . just unlikely.) Plus they and druids never built towards spells - they'd get the 1-2 they needed but generally need ER and FP and PI more than they need to fill out a giant spell list.
I did put it on wizards because of my experience with my previous campaign, which featured most of the same players.
In that game, every wizard pretty much was a slightly-different version of the other wizards.
Oh sure, Ol' Cort had Lightning and Body of Air, and Crestlin had Stone Missile and Hawk Flight. But the mainstays? Everyone had Teleport, Great Haste, all of the healing spells, See Secrets and other utility spells, and so on. Even one of the non-wizards used a Great Wish to get Magery so he could use Hawk Flight and other high-end movement spells.
In my games before that, it was the same. Wizards were people with Teleport, Great Haste, Levitate, Major Healing, a missile spell of choice, Dispel Magic, and a few others no one left home without. Didn't have them? Then you weren't a PC, or you had Magery 1 from being an Elf or something and couldn't.
And it goes without saying, a wizard without Missile Shield or Levitation almost isn't a wizard at all.
Fast-forward to DF, and I forsaw players making the same basic mage and then spending 4-5 of their 4-5 points a session on getting new spells. Nevermind a slow crawl towards spells they felt most aided their niche or their existing choices, it would just be "In two sessions, I could have (pick spell name) and we could come back and solve this problem with it."
Since I already have a lot of frustration with people using GURPS Magic as a shopping list for solutions to game problems -
"Let me find 1-point win button spell for this problem" - I figured, well, limit them to one spell and you're mostly fixated on what you can do with what you've got.
Take the brakes off, and wizards would be more fixated on spending points to get a variety of spells that could cover anything and everything.
Plus, it means the other players have a legitimate beef with you if you don't spend all of your points on getting spells that could be useful. Hey, you can get 4-5 spells a session, so "I need 8 spells to get this spell you'd like me to have" is merely you putting up your points for two sessions.
However, despite my concerns, my players are pretty much convinced these things won't happen. I'm not sure, but it's our game, not my game, so we took off the brakes.
On the plus side, this might mean the end of "I'm a fire mage" and "I'm a mind control mage" and "I'm a movement mage." It's much easier to end up an Elemental-spell mage or a Save-Or-Die mage or broadly-skilled utility mage with more spells available between each session.
It does mean I'll need to pay very close attention to spell choices. At 1/session, I don't - I know far before you get Mass Zombie that I need to tweak its prereqs, or before you get Earthquake that I might say it's unsuited to game. I only need to answer one question about spells each session. Now I'll need to answer many, as people ask "Can I get (spell name)?" and I need to check it and its prereqs for issues, and then answer the same question about another as my answer changes the desire to have it ("Nevermind, I'll get (spell name) instead, okay?")
There was a suggestion of a mid-point, but I found that even more annoying - why 2, or 3, or 4? Why half of your earned points or anything like that? That takes even more thinking than "all or nothing." The only addition I put was - if you buy multiple spells, you can't be doing extra stuff in town. No finding hirelings, doing Research, Carousing, etc. You're busy cramming spells, finding folks with those spells, reading weird books at the Wizard's Guild, etc.
So we'll see where this goes. I have very strong opinions about this, but again, our game. The players really liked this change, and we'll see how it goes. Hopefully it's more for the good, and the style of DF lends itself to a different outcome than I had in my 1e and 3e games. If not, well, DF is the game to find out in. It's high powered and pretty fault-tolerant, in my experience.