For example the preview of a Browser window uses 5% of my GPU and 0.38% of my CPU.
Deactivating the preview I can reduce this to 4% of my GPU and 0.38% CPU.
So if you think thats worth it. Go for it :)
(Side information, I only ran a preview with encoding disabled to measure the pure OBS usage in this case, slightly higher GPU usage might be noticed when there is a lot of action going on. Resolution was 1080p at 60fps)