We've had a similar sort of discussion before in
Short skill list - who likes 'em? What I've found is that most players are not grognards, they're not into every detail of the system. They tend to be looking up, around them at their fellow players during the game session, and don't look at their character sheet much.
This means that of what's written on a character sheet, only about six or so things will regularly come up. Those things could be skills rolled for in play, some disadvantageous character trait the player really plays up, some outstandingly good or bad attribute, and so on - but basically only about six things come up in play.
It seems to be a common experience, that there are dis/advantages and skills utterly forgotten, and very minor ones which
become very major just because the player plays them up, and so on. And then of course there are the things which aren't written down on the sheet but the player insists on them anyway.
"Just kill the guy, you know he's half-demon."
"No, that would be murder! I can't do that, it's against the law."
"Your character doesn't have the trait "law-abiding"."
"Yes but that's what he is anyway."
So in
principle you only need on the character sheet those six or so things, you may as well toss out the rest. But in
practice exactly what those six things will be in play isn't known during character generation, and players want the choice.
As well as giving them choice, it sometimes gives players happy surprises, as Morrow described on the other thread,
"Years ago, we were playing a homebrew magic and technology game. Two of the PCs were in combat with some bad guards trying to kill them. One PC is a master at gun combat gets his gun knocked out of his hand after a few rounds so he draws his sword, which he's also pretty good it. That gets knocked out of his hands, too, after a few rounds. His character gets the snot beaten out of him for a few rounds fighting unarmed and unskilled and suddenly the player looks up from his character sheet and exclaims, "I'm a grand master in unarmed combat!" He hadn't used that skill in the game and forgot he had it."With just six things, there'll never be any happy surprises
But you may not care about that.
So, having a short list of skills and other traits will ensure you have a brief character sheet, and will mean that the character is well-defined to begin with; whereas having a long list of traits on the character sheet leaves the player free to develop the character in play, focusing on the bits they think are fun or important.
What came out of that other thread was that if the skill list is too short - about a dozen - then really those aren't skills, but character classes. If it's too long - over about a hundred - then there'll always be some skill which pops up needed in play, and a player gets pissed off, "but my character would definitely have taken this skill!" or else nobody took it at all and the game comes to a boring stop. So the longer skill lists can work if the GM is generous in which applies to what, or if they have generous defaults to each-other. "Okay, you don't have lockpicking, but you have clockmaking, so you understand the principles of little bits of metal moving each-other around, um, half your clockmaking skill you can use as lockpicking."
The other aspect is that if you have a long campaign, you may want long skill lists to give players something to fiddle about with in character improvement.
But then, long skill lists sometimes mean you end up with a very long character sheet. I remember playing Rolemaster, taking a character from 1st to 6th level, I went from one page of skills (one per line) to two pages. And honestly there were only about six skills that ever got rolled more than once.
I settled on 30-40 as the ideal number for players to choose from.
I'm not fond of "define your own trait" things. It relies too much on the creativity of players as individuals. And creativity varies a lot between people, and a lot between days - anyone can have an off day. It's better to have a list to choose from - if only for inspiration.