I would like the ability to disconnect Transmission from the Internet, while it remains running.
This is especially helpful when verifying local data - seems like it goes faster when I turn Airport off, so Transmission isn't trying to download and verify at the same time. Of course this stops me from doing anything online.
For whatever reason, Transmission seems to lose track of local data a lot, and frequently when I open the app, or sometimes when I reboot or reconnect my external drive, it has to start checking the data in some or all running torrents.
Sometimes I need to open Transmission to check out which files have completed or for another reason, but don't want it connecting to the Internet because it drastically slows my connection speed.