Originally Posted by Helmet Head

Exactly.

Say someone came up to in an alley with a gun pointing at your head and made the following offer: "I will shoot you in the head, OR, I will let you toss a coin and if it comes up heads I won't shoot you and will leave".

Do you agree to toss the coin, even though doing it "may or may not have had any use in this situation"?

The two choices are:

a) Ride in the bike lane.
b) Ride centerish, move into the bike lane only when fsdt is present or approaching.

To me, (a) is analogous to refusing to toss the coin, and (b) is at least giving it a chance.

The difference is that inadvertent drift/swerve is so unlikely in the first place that doing (a) or (b) will almost certainly not make any difference in any given situation.

However, if you ride for years and years and thousands and thousands of miles, your chances of encountering a driver approaching from behind who is about to be distracted by something increase with time and miles. It seems to me riding in a manner that increases the likelihood of such a driver to be aware of you presence before he gets distracted only has a plus side. More importantly, riding centerish makes it less likely that you'll overlook a potential cross traffic conflict up ahead, which is more likely to cause a crash than are threats from behind.