This feature allows you to slow down the application by setting a small sleep-time the CPU may uses between two consecutive operations. Although it may sound counter-intuitive this feature is actually helping you (likewise Upload throttling) by not using 100% the CPU during backup/restore operations.
With other words although your system is engaged in a resource consuming operation (like backup/restore) your website visitors will not notice a thing because it is you who set how much CPU will be used and thus how much will be available for your website visitors.
For instance, if you set a CPU sleep time of 1000 ms (ie. 1 second) then the backup/restore function will compress/decompress a chunk of ~4KB then sleeps for one second. Then it continue with the next chunk and so on. By doing this the system’s CPU will be almost free (not used) which means that it is instead available for your website visitors.
When you want to disable this feature just set this option to 0ms which means no-sleep, ie. 100% CPU.