It hasn't forced the server to ever transcode anything, either, handling everything natively. I haven't had any problems with any of this via any service, including Plex, on the Roku Ultra. Part of the reason I bought it was because my old device didn't do Dolby Digital Plus (which is the format that the lossy/bullshit version of streaming 'atmos' gets plugged into) a lot of basic 5.1 and even stereo stuff is starting to use it, though, so it forced my hand.

I often leave it off unless I'm doing a movie or a binge-sized tv session where there's no menu usage. It's just good to have the option as I hadn't had it for a while. When the plex client is on Auto, the video is transcoded (even though bitrate limit is set to 20 in Roku Client) and audio is transcoded to 5.1 Dolby Digital. The best feature is native support for 24/30hz playback, although the handshakes every time you use a menu item get annoying. Playing back MKVs via Plex seems to add a bit more audio delay (~20ms?) than playing back the same files via USB on the same Roku. I have no idea what the Roku included in your TV hardware is equivalent to, though. Icons for my music library actually load faster than Chrome can do it on my PC.

The plex layout is a bit better on Roku than the firetv, imo.

Plex media server roku transcode