There is no advantage in gameplay (glitchless category), but in Source Unpack you can install the Auto-Recorder Plugin which basically just automatically starts demos (You can find that in the resources tab - https://www.speedrun.com/Portal/resources). Also if you have more questions I'd recommend you to join the Discord: https://discord.gg/EwTmb3a

The main difference for glitchless would just be performance. When you save or load in steam version you get big stutters, this doesn't happen in source unpack,