Doing it in front of a cop adds flavor.

Just shows me you're not familiar with the area, nothing to be ashamed about.

Or when you're new to an area, know that those deceptive lanes are there, but forget which exits use them... so then you stay in the center lane because 'that's a fake merge lane!' but then 15 seconds later "motherfucker I just missed my exit!"

At least you're making the traffic flow faster, no?

No lane switching slows traffic down

Not in this scenario, where the optimal traffic flow is merging at the point where the two lanes actually merge and not before that.

Assuming that the other cars aren't using that lane to capacity, yes. Otherwise, very much no.

My city built a new tunnel, below town, and the entrance was at a stupidly complex intersection. I swear to god the lanes changed every other day. I live and drive here for over 20 years, I still ended in the wrong place multiple times across the last few months.