Learning Skills/Spells innately vs. Buying them from shops

I'm sure we've all seen both ways of doing this. In some games, characters learn their new skills or spells as they gain levels. In others, you arrive at the new town and go to the magic or tech shop and buy some of the new spells that are available.

My question for discussion is: what are the pros and cons of each? When designing a game, what factors do you consider when determining which system is preferable for your project?

A linear skill learning is better for a linear game with linear progression. That what you do is to continue the game progress.

Buying a new skill (either by shop or menu) is better for teasing a player that you have to grind this and that. There are rewards waiting for you if you grind enough "currency" to buy them. It can be for linear progression or one that have "customization".

I think it all depends on how much you want to emphasize the skill system and learning skills in your game. Auto-learning on level up places the learning of skills far in the background, as it requires no effort on behalf of the player other than continued progression. Learning skills in shops adds a bit more interaction and either some degree of customization (can't learn everything, so pick and choose) or a way to reward players for exploration (rare skills available from hidden/out-of-the-way sources).

The approach I'm taking is a combination of "each character has a skill or two learned initially" combined with "characters gain JP on level up which can be spent to unlock additional skills from that character's overall skill list--no prerequisites, so which skills are entirely up to the player." There's also "skills temporarily learned by equipping certain items," so the player can buy Fire from a shop and use it, find Ultima hidden in some secret part of a dungeon, etc.

I think both systems are great depending on the style of the game and open up different avenues of customization, if you are looking for that kind of thing.

Learning skills in a linear fashion as you level up is generally great for games where you want a large party that encourages switching members around to find your favorite team composition. This can also let you make more focused and distinct playstyles for party members, which could lead to some unique gameplay opportunities.

A system where you need to buy or manually learn skills (such as games that use a JP system) lends itself to a smaller, fixed party but with a higher degree of options in skills to learn. This allows you to fully embrace the customization options it brings without becoming overwhelmed with designing many skills for like 10 party members. This kind of system is a blast to toy around with and try and come up with your own broken strategies and can lead to some very satisfying fights.

To me, it boils down to where you want the customization to be. Both can be great when used to their full potential. Personally, I am having skills learned as a linear process, as I wanted to emphasize the unique abilities each character has and found that trying to incorporate a less linear skill learn system kind of made it a bit much to keep track of, both for me as a developer and for my players.

In a game I have planned, each character is going to be learning skills in a different way. One character will learn them by gaining experience in battles, while one might have to go to a trainer in each town to learn a new skill.

I feel like tying the skill progression to each character's individual class and personality really fleshes out that character more and adds individuality and variance to the game.

*learning* skills allows for some customization, while *acquiring* skills doesn't.
from there, you can use that (or not) to help develop the characters, story-wise (characters might deviate slightly from their stereotype based on how the player chooses their skill allocation)

recently I've played Baldur's Gate, and it happened to me that one character could multi-class, so I went "oh, let's multi class, for the funsies".... and I couldn't go back to the base class until the added class was equal in level to the base level, so effectively now I'm running 2 levels behind everyone else in the party, and I can't improve the base class anymore.
that wouldn't have happened if the progression had been linear.