I believe they're blocked off until the flight nears capacity as part of routine weight and balance management. But I might be wrong.

I flew in row 1 of an Air Wales ATR-42 (serial number 329, now operated by Calm Air in Canada) in 2005. It's a fun experience, especially take off, but it has the significant disadvantage that you spend the whole journey making inadvertent eye contact with the rest of the cabin.