I think they use those for aerodynamics also. But yeah they turn up in spring and summer. Not much outside those seasons.
I find them very annoying, they tend to be very inconsiderate. Cycling on the road where bike lanes are available, and when they are on the bike lane they tend to be agressive to normal cyclists if they don't move along as fast as they want.
They're not all like that but many of them are, which leaves a bad taste as soon as you spot these groups of wannabe lance armstrongs :P
I don't think helmets are worn for aerodynamics. IIRC professional race cyclists only started wearing helmets after in 2003 when they became mandatory. If there had been any advantage in aerodynamics the athletes would have voluntarily picked up helmets before.
Also, anecdotally, I am occasionally road cycling for sports and do wear a helmet at all times. However, I am certainly not doing that because of aerodynamics.
I find them very annoying, they tend to be very inconsiderate. Cycling on the road where bike lanes are available, and when they are on the bike lane they tend to be agressive to normal cyclists if they don't move along as fast as they want.
They're not all like that but many of them are, which leaves a bad taste as soon as you spot these groups of wannabe lance armstrongs :P