If you're stuck in traffic for a long time, your leg engaging the clutch can get very tired. So you're constantly switching to neutral to rest your leg.

It's also not uncommon for traffic to go from stopped, to fast enough to warrant 2nd gear, back to stopped.

In my experience that is not the case. Specifically because jams are waves not just slow moving traffic. A gap will open up and quickly I can be in the 3rd gear to catch up. Of course as soon as I do the flow stops again. I could just creep forward in 1st and let the rest of the flow fill in front of me...

Manual transmissions are definitely hell during rush hour... but doesn't seem to affect people contributing to the waves in my experience.

you will ruin your clutch bearing way faster. it's much better to keep constant speed (for engine/gearbox and for traffic in general). plus - you can't drive on highway on 1st gear. you still need to switch to upper gears.

Hm, just so you know, never drive in first. That's just the one to 'start'. Either, you'll kill your engine too early. Engaging the clutch every 10 meters is what is irritating. That's the point !