Okay, let me try a review of the Risk matrix.
low probability x mild consequence = low risk
High probabilty x mild consequence = low to moderate risk
low probability x bad conseqeuence = moderate risk
high probability x bad consequence = high risk
With varrying shades all through
(Note: I am using the general 'you')
Now the odds of something bad happening because you asked a stranger to look after your bag at an airport are low, very low. But the possible consequences of doing so can be very, very high. Anything that stranger does to your bag you are liable for and having something stolen out of your bag is really one of the most mild possibilities.
Probability something bad will happen: low
Possible outcome: Very, very, very bad. (Including theft, accusations of theft, ID theft, suddenly finding yourself responsible for holding drugs or weapons, and of course the negligible but still present threat of terrorist dangers.)
Watching someone else's bag or asking them to watch yours is a very high risk.
Add to that risk that there are airline employees who will only give you about a minute window to return before alerting security.
TSA is not nearly as effective as we all pretend it is. Do not let your bag out of your sight.
If your bag is too large to take to the restroom or to get food/ magazines, then please check it.
(Note: this is one of my 'issues.' So take with as much salt as you like. )