Another example is you don't have a seat assignment on at least one leg, and you check in...this places you on the standby list for a seat assignment, which means you don't appear (at least on the app) on the UG list until you have a coach seat assignment.
If you call, uncheck, pick any seat, recheck in, you will then magically appear on the UG list. ^
Some SLC supervisor kept warning me that my position on the UG list could change...as if check in time is important (if at all) for UG list position...I still proceeded, was #1 to start, and ended up #1 at the gate and cleared.
There may not be security issues as far as you having anything not allowed on you passing through the checkpoint, but why would you be at the airport and past the gate if you aren't boarding a flight (barring IRROPS or emergencies where you would have to leave?).
A close friend runs multiple states for TSA, and recently told me that TSA is specifically looking for passengers that (frequently) purchase tickets, pass through the checkpoint, and don't actually fly. Obviously they have access to airline records as to who boarded a flight. So I certainly wouldn't make a habit of it, nor would I assume "no security issues."
Because it is the government after all, and if they wanted to give you a hard time...reminds me of what Bill Hader's character said in Superbad..."prepare to be f***ed by the long d**k of the law."