I started gaming with AD&D. I just accepted that split XP charts were part of the game. I assumed that some meticulous carefully balanced extremely well tested methodology was used to create these charts.
Then I learned more about the creation of the game.
I think it was much more haphazard. "Hey, Gary, thieves suck a lot." "Well, lets just give them a quick XP chart, that'll balance it out!"
I don't like it. First, its an obscure mechanic for something that should be clear. It'd be better if it said right under class abilities: "FAST LEVELING: THIEVES gain a bonus of +20% XP whenever experience points are earned." Instead, that crucial balancing factor is hidden in the XP table where the casual reader may not notice it or understand its import.
Second, its a very fuzzy mechanic that seems to conceal the real problem -- a lack of balance between the classes. "Well, the wizard rocks a whole lot more than fighters at higher levels, but its ok, because he has a slower XP chart." The next question one must ask then is, "Well, how much slower?" and "What if I added, say, minor spells to the fighter?" And that road leads to much nonsense and knashing of teeth (Case Study: TLG's Castle Keeper Guide). Because at some point, it becomes clear that no amount of painful XP chart balances out the absurdity that the class has become (Case Study: AD&D UA Barbarian).
Third, it precludes using simpler levelling techniques. For example, if the GM wants to say, "Ok, everyone gets a level now" at an appropriate time between quests, he's really screwing over the people that have quick XP charts and throwing an unintended bone to the folks with painful XP charts.
So, I much prefer to strive for a unified XP chart, which means class balance. This is hard. Basically, you must sit down and for every level determine how effective character should be against a given challenge on both the micro level (round by round within an encounter) and the macro level (over several encounters or even an entire quest). Then you tone up weak sauce or tone down strong stuff.
As an aside, this is hard to do with Vancian magic, because one overly potent spell or combination of spells can blow the entire curve out of the water. This was the undoing of 3.5's unified XP table, among other things (Case Study: CoDzilla).
ADDENDUM: LEVEL LIMITS
Level limits for demihumans is another "balance" cop out, IMHO. For example, old school dwarves pretty much are fighting men that are better. Except they top out at a certain point. So, a rational actor has two options:
IF you think the campaign will not extend past the level limit, then the demi is strictly better.
IF you think the campaign WILL exceed the level limit, then the demi is a dead end and is not a viable option.
One could slap an XP penalty on the demis to pay for the extra abilities. But, that leads to the above issues. So, you really need to tone down some aspects to pay for the goodies, or tone up the Fighting Man.
OD&D Experience Levels
8 hours ago