Eve Online's time-based skill training system is probably the most obvious example of limiting the advancement of a player's skills. Eve is a skill-based, not level-based, game and skills are learned in real time whether a player is logged into the game or not. Many people complain about the system because they cannot advance their skills through their game play. I actually like the system because I don't have to do certain useless things in order to become better. For example, the skill system keeps me from having to make a lot of useless items in order to become better at manufacturing. Another advantage is that I can work on my missile skills while running a cargo of blueprints through low-sec. But while the skill system does have benefits for players, the system also keeps players subscribed even when interest wanes because players can always justify the subscription price because they are still training wanted skills.
Most other MMORPGs are level-based, not skill-based. One law of MMO development is that players will always run through a game's content faster than the developers can create it. So the trick for developers is to make a game that is so interesting that players what to hit the level cap and raid while at the same time don't want to play for hours every day and quickly burn through the content. Blizzard's Rob Pardo came up with a solution.
"In World of Warcraft what they did when they first designed the game was they had an experience system that would, over time, lower the amount of experience you got because [Blizzard] wanted to encourage people to play for like two hours at a time instead of twelve hours at a time. So the longer you played you’d get this experience degradation and then it would bottom out and at that point it would be a fixed rate of experience. And people just hated it.
"And so they went back and [Blizzard's Rob Pardo] was like allright, basically what we did was we made everything in the game take twice as much experience to achieve as before and then we flipped it. So actually what happens is you start getting 200% experience and eventually it goes back down to 100%. So that effectively now how they spin it is that if you log out for a while you get this 200% boost when you log back in! And then over time it goes away and you just get regular 100% experience. It’s EXACTLY the same as it was before, except NOW everyone is like 'Fuck yeah, Blizzard, this is exactly what I want!'"While the system doesn't keep a lot of players from hitting the level cap in WoW quickly I know from personal experience that when I saw by bonus xp about to end in both WoW and EverQuest 2 that I knew it was time to stop playing for the night.
What worked for games published in 2004 is still used today. Star Wars: The Old Republic uses a rest bonus xp system if a character logs out of the game in a cantina or a ship. But from my experience, the rate of the bonus seems to be about 1/2 what I received while playing in old Vanilla WoW or in EverQuest 2. That could be because BioWare is concerned with keeping players subscribed after their free month for buying the game is up. I'm currently playing the Smuggler class story and am finding that just playing the single player elements after the rest bonus expired had me on Tatooine a full level below the recommended level. That has led me to not only spend hours grinding mobs to catch up but to also not play as much over the last few days.
Yes, SWTOR is a multiplayer game and that means I should play with others more. But BioWare is really depending on players to play exactly through all the story they created. Anyone who tries to skip part of the story is going to encounter hurdles. That's fair, but then again I've played MMOs for over 6 years now. I wonder what all those players who are jumping into the genre for the first time because this is Star Wars think. I'll have to pay closer attention to the chat to find out.