My first World of Warcraft character to hit level 60 was a troll warrior. But sometimes I regret not having made a gnome warrior instead, because I really like playing short races. My troll just doesn't look good in plate armor, while the same armor looks much more impressive on a gnome. I'm happy that in Lord of the Rings Online my tank is a hobbit guardian. But the really surprising thing about those choices is that the effect of your race on gameplay is so small.
If you play classic single-player computer role-playing games, like any of the Might & Magic or the Wizardry series, or if you play pen and paper D&D, it is very obvious that a troll, half-orc, half-giant or whatever big and strong races the game has is far superior as a warrior than a gnome or hobbit. From the small races only dwarves usually make good warriors. Making a gnome warrior in most games would be a serious penalty, you would basically gimp your character. But in MMORPGs like World of Warcraft it doesn't really matter. The difference in stats and abilities, especially at higher levels, is so tiny, you'd have a hard time to measure it.
This isn't immediately apparent if you look at starting stats, where for example a troll has 24 strength versus a gnome's 18. But that difference doesn't go up with level, so at level 70 in the same gear the troll might have 524 strength versus the gnome's 518. The only real difference between races are the racial traits. And while the troll racials are arguably better for a warrior, the gnome's escape artist is certainly quite useful for a warrior in PvP. There is a difference, but it isn't really big enough to matter. Nobody would turn a gnome warrior away to take a warrior from some other race with similar gear and experience into his group. Race, which used to be an important characteristic in earlier RPGs has become something that is mostly cosmetic.
The reason for that is that word "gimp" I used earlier. My first Everquest character had the wrong race for his class, plus at the very start I had to distribute stat points and did that in a wrong way, based on bad information in the printed manual. By the time I found out how the game really worked, I noticed that I had gimped myself, making my character noticeably weaker than others of the same class and level. And, there being no way to repair that, I started over with a character of the same class, but a more suitable race and all the stat points distributed to where they should be. At some point in time between EQ and WoW game developers decided that the ability to gimp yourself was not something they wanted to have in their game. Instead of allowing any race to play any class, but some races being better at some classes, they just made all races nearly equally good for the classes they could play. And they simply disallowed the combinations they didn't want, like gnome hunters or orc mages.
Is preventing players from making bad choices a good idea? It does make the game more accessible to people not used studying guides and websites before jumping into the game. But it also makes these choices uninteresting, because they simply don't matter that much. It is hard to imagine how a game could allow you to change your race later in the game, so making the choice of race matter a lot risks setting up a trap for the unprepared. But I liked the elegant solution of Final Fantasy XI, where your choice of race was final, but you could always change your class. You'd lose your level, but not everything else, so if you found that a Taru didn't make a great warrior, you could still continue playing him as a mage. I think it is okay to allow players to make bad choices, as long as there is some way to repair it at a penalty less harsh than deleting your character.