OK
I think its fair to say that all the reply would fall into the category of 'they are there for a safety reason' - be it warning of some danger, telling you where on the road you should be, etc etc
If this is correct - then why do they not paint white lines on ALL roads?
I know that there are lots of country roads without lines - but we still manage to stay to our own side of those roads, navigate round bends etc
But where I used to live, on a main thoroughfare road, houses one side, playing fields the other, a school along the road and several joining roads, there were no central white lines :dunno:
I personally think that they can at times promote a feeling of 'safety' in the road user. I'm on my side of the line, so I'm safe!
Roads without a white line require a little bit more concentration.
So, ban the white lines? As Rhino said 'they make your bike twitchy in the wet, so how can that be a 'safety' feature?