I think PreCheck has some distinct advantages, even if it's "PreCheck Light / Expedited Screening:"
- No body scanning unless it's a really bad day and they've unwisely decided that random alarms go to the AIT. I always seem to set off the "Advanced Imaging Technology" scanner, but I never set off a metal detector. The metal detector is much quicker and far less annoying.
- Shoes on. This saves a lot of time, and it's arguably less disgusting. Also, I don't trip as much.
- Zero chance of a "quad" or "SSSS" for flights within the USA or departing the USA. It doesn't work the other way around for some moronic reason.
- The PreCheck queue is much shorter most of the time.
- CLEAR gets an escort to the front of the PreCheck queue in most cases (definitely at T1, T2, and T4 at LAX, PHX, DEN in recent experience.)
- Unofficially or unannounced, no security interview on AA flights from Heathrow, supposedly to expand to other airports for PreCheck passengers. Yay.
- Somewhat expedited screening in Canada for Global Entry/NEXUS. I'm not sure about PreCheck as a standalone product.
- Unless it's "managed inclusion, (Arf! Arf!)" PreCheck passengers tend to be frequent flyers, and they're not as prone to fumbling through security. This is variable, but there aren't quite as many people wearing iron Viking helmets or underwear made of aluminium. (I've totally left my headphones around my neck like an idiot, so I will be refrain from judging those who make unwise choices before going through a metal detector.)
- Arguably less yelling and barking. Since PreCheck passengers tend to be veteran travellers, the staff are usually a tad quieter in the PreCheck lane. Not always, but most of the time. They can even be outgoing and friendly on a good day. I get the impression that the TSA staff like PreCheck. It's less work, less hassle, less touching of gross people, fewer rules to enforce.