What advantages are there to playing with a locked camera?

I'm surprised nobody mentioned the spacebar.

If you are an experienced player I would advise against playing with a permanently locked camera, however that doesn't mean you shouldn't use the lock camera feature at all. Also if you feel comfortable with a constantly locked camera you can go ahead and use it. I know high diamond players that play with a permalocked camera.

Now in general I'd recommend using the spacebar in order to lock and unlock the camera. By default the spacebar locks your camera temporarily while you hold it down and unlocks it as soon as you release the key. This allows you to look around whenever you want and if you get involved in a messy teamfight you can just hit down space in order to lock the camera and get a better overview of the fight.

Space as a key comes especially handy since you won't use your thumb for any other key and the default permanent Lock/Unlock button is on either Z or Y (depending on your Keyboard layout).

Although using Space to freely switch between locked and free camera is extremely effective you still have to keep in mind that changing your camera behavior is a huge shift in your playstyle and you should practice it first.

If you play with the camera always locked, you'd lose awareness as for trying to see what's happening below/behind your character. Also it's annoying when you have dashing champions around OR if you're using one, because it won't make you easy to aim properly with your mouse, specially if it's about skillshots WHILE you're moving with the camera together.

While I'm playing with the camera unlocked, I use the spacebar so that I can be aware of where am I walking.

The "camera locked" feature is only for people who don't want to get lost in the map (or messing around with the camera as Yuuki said) when they barely start playing these kind of games. Once they develop some experience and realize (from experienced people), they'd release the camera eventually and get used to the space bar whenever they feel lost.

I would consider myself an experienced player. I have been playing League on and off for about 3-4 years and I play with a locked screen about 90% of the time when in game.

It is quite possible that the reason I have stuck with using a locked screen for so long is because of habit and fear of change, but I can't deny that I find there to be several benefits to using it.

The main benefit to me is reliably following my champion and not having to worry about moving the screen. I'm quite a paranoid player so I would hate to accidentally walk into a fight while my camera is off elsewhere, or having to mess around with adjusting the screen because a team fight has moved out of the view of the camera.

However, that doesn't mean that a locked screen should be used all the time. The other 10% of the game is unlocking to look at certain events, typically for scouting purposes. For example; I will regularly unlock to watch team fights I am not involved in(this is so I can see the general performance of the team and to see if it is possible for me to join the team and help/pick off survivors). Another example would be to watch the enemy team fight Dragon/Baron, to see if it is possible to steal or engage on their possibly weakened team.

Other possible reasons to unlock would be for general vision of the game and when using long range/global ultimates.

I really wouldn't advise anyone to play locked permanently, as it makes the above benefits very difficult/impossible.

In conclusion, I play with a locked screen because I find it removes the need to constantly re-position the camera and because I have gotten used to it, but also unlock the screen to benefit from scouting and using vision to make important decisions throughout the game.

Locked Camera Controls are also very good for Pickup and Play style games. However, I do not find League of Legends to fall into that category. This also makes it easier for you to have more precision with your mouse and control your skillshots.