If you are Mosaic or have the Even More Speed option, you can use that line as a backup.

I've had 2 experiences in the past week where the Premium line was faster than PreCheck.

1. Last week at ORD, the PreCheck lane on a Tuesday afternoon was at a standstill with at least 50 people on it. I used the L Concourse security instead and they let me keep my shoes on. I was through in less than 5 minutes.

2. JFK T4 this past Monday. I was on the PreCheck line for 15 min but Delta Sky Priority pas were walking right through.