this is another interesting feature you can enable. when you record automation, an insane amount of nodes are created and it can make the automation line unwieldy. you can hold shift as you drag a node to delete the other nodes it comes into contact with, but this isn't a very elegant solution. what the "thinning" is doing is removing nodes to make it simpler. the default value is set at .45 but the higher the number the less nodes and more "smooth" your automation will be.

enable by entering the following into options.txt:

-ThinningAggressiveness=0.85 (or whatever number you feel is appropriate)

there's a lot you can do with options.txt, most of it for very particular circumstances. you can read about it from ableton here and sonic bloom's excellent tutorial series here if you want to know more about what you can do.

high quality/oversampling modes