Dashcams stop you getting done over in crash for cash scams.
I have to wonder sometimes with the way people pull out of a couple of fuel stations near me whether they are trying on crash for cash scam - I think most of it is just lazy, inconsiderate and uncaring driving. The one time I'm 99% sure it was an attempted scam they definitely had second thoughts - as I was driving a large black pickup and had my high-viz on from work still they probably thought I might have been unmarked police or something.
. I thought by default anyone hitting your rear end (ooh Err Mrs) had to prove you were at fault, which in theory is impossible as you should always leave a gap.