I'm in both group 1 and 2 (I normally alternate between the two, i.e. soap - water - soap - no wash - soap...). Washing with soap removes oils. This is a prett

I'm in both group 1 and 2 (I normally alternate between the two, i.e. soap - water - soap - no wash - soap...). Washing with soap removes oils. This is a pretty obvious effect from anyone who's ever tried to clean up oil/grease with soap (ex: dawn). Rinsing with just hot water distributes oils from the scalp down towards the ends and it removes a little bit of oil in the process. Rinsing with cooler water is less effective at distributing oils but also loses less oil in the process. Not washing allows grease/oils (and skin/dander) to build up on the scalp and saturate hair near the scalp. ----- If you are just rinsing/scrubbing with water, it does a lot relative to not washing at all but there isn't really a comparison when it comes to soap's efficacy at stripping oils/making them semi-water soluble so they can be washed away.