I have a rol bar thats bolt in, wouldn't think of taking it out when using the car on the road.
Also wouldn't wear my helmet when on the road, but i do use my 5 point harness.
My thoughts are that if anything did happen the harness would keep me in the seat and not to much body movement.
When having a roll bar fitted make sure it has clearance above your head, this would allow for the extra space needed for your helmet if your are wearing it.
Roll bar padding is neaded on any part of the roll bar that your 'helmet' may strike. So surley the extra space means that if you are strapped into your seat with an harness the chances of hitting your head are reduced?
If you are going to the trouble of having a good quality roll bar fitted and don't bother with an harness of good quality what the point?
'For show'
You may also want to think on how good the roll bar if fixed to the car?
Insurance companies may view most people that fit roll bars as only doing half a job?
Just my thought on the subject