Differential locking is a highly tuneable thing and has great effects on the handling of the chassis into, mid, and out of the corner. Think of this as power on, power off, and neutral throttle.
For a traditional touring / formula car:
If you're loose on entry, but okay on corner exit, you'll need more entry locking
If you push on corner entry, but exit okay, you need less entry locking.
If you're good on entry, but push on corner exit, you need less locking.
...
and you should get the picture. Obviously there are couple aspects to tuning it, but how much lockup and the rate of lockup are tuneable for most racing set ups. There are of course drag considerations to consider, as well as chassis and the type of track as well. A Formula Atlantic or something with less power on a fast smooth track will use less lockup to reduce any tire scrubbing. Of course, there is this feedback to loop to consider as an optimum differential set up, that maximizes grip and minimizes tire scrubbing may require an entirely different chassis set up (within a certain window).
Electronic diffs add all new elements to tuning as well.
With electronic throttle bodies, you throw another element into it as you can tune the amount of engine braking you have as well, which will effect corner entry and neutral sections. This is more commonly discussed in motorcycle road racing circles, where they will tune engine braking to the rider's preference, and they can tune it based on speed / location / etc. They do this by controlling the throttle body opening and throttling with a combination of fuel and ignition cut. It's much easier to also control the engine braking, as it's going to occur at a non linear rate. Furthermore, it comes down to rider preference, with riders growing up on 2 stroke bikes preferring less than riders who came from the 4 stroke, dirt track type world. Old 2 stroke dirt track racers would add engine braking by using the decompression lever, on purpose, especially in the brakeless classes.
. This is something you can actually tune with some of the higher end Sportbikes off the showroom floor, which is pretty cool. You can see how much more riders on bikes use this to rotate the bike on corner entry
Cars don't have as much engine braking problems due to more rear traction, especially cars with downforce. HOWEVER, it can be used in conjunction with the differential to influence factors as discussed above.
However, in thinking of a per corner basis, some corners will want more lock up in certain places. A tight corner may want more lock up on the way out as you will be accelerating hard and in going slower, you'll have less downforce to play with. A fast corner you may want less lockup to reduce tire scrubbing.
