Disclaimer: I suck at judo
Uchikomi is a huge help to me. It trains entry to a throw, which is arguably the most important part (assuming that you dump the guy on his ass at the end). And since I still have relative noob status, decent throw entry is difficult for me during randori.
Specifically, moving uchikomi is the most helpful to me because you have to enter for the throw in a somewhat realistic way (not static). Also, it's good to be able work on combinations without getting thrown if my sweep wasn't perfect.
And, in response to the arguement that you're not practicing the throw as you would in randori, isn't the idea to improve your technique? The more you practice a throw (in realistic circumstances), the better your technique will get and the better you'll be able to perform it during randori.