While I completely understand @SE13Mummy's stance, I do feel there is some merit in having the threads on a forum like MN - one poster has already pointed out that she took notice of info from a thread to go to A&E when she had the same symptoms, and turned out to have sepsis.
I have used it before, despite having some HCP background, when I got something stuck in my eye in the middle of the night - I was going to leave it but was advised to go to hospital (which I did, but I drove myself)
111 isn't always great in speed of response - I know myself, I used it for my grandfather years ago, when he was in great pain. It took them forever to call back, by which time he was almost crying with pain, and they were trying to insist that they had to talk to him directly - EVENTUALLY they sent an ambulance. He died a few days later in hospital from a perforated gallbladder and further complications.
So I can understand why people post on here - they may think that it's trivial, and there is a wealth of personal experience on here that can be tapped to show that it is/isn't; but I TOTALLY agree with the OP that there should be a standard MN caveat attached to ANY medical-type post.
Sometimes you just can't wait. I took my 3yo to hospital with strange symptoms, despite having called the GP, having seen him the day before as well - because I couldn't wait for him to call back. Good job I did - the child had appendicitis with a black and gangrenous appendix which was removed first thing the next morning.
I remember another poster who had a DVT - she posted quite casually to start with but enough people warned her what it could be, and how dangerous it could be, so she went to hospital and sure enough, it was a DVT.
Ectopic pregnancies - another example of people who have been helped on here.
But again, I totally agree that the "Do Not Call An Ambulance" crew should really keep quiet. There are far too many "I don't want to be a bother" people out there who would take that as the only comment worth paying attention to, despite 99 other comments telling them it was potentially very serious and they should go to hospital - and that could potentially be fatal for them.
Agreed that genuine medical professionals shouldn't/wouldn't be posting definitive advice either, and I'm sure they don't - so if someone claims to be one, and is doing precisely that, then chances are they aren't genuine. The only medical advice they would offer safely is "get seen by a medical professional" - which may involve an ambulance!
My own sister called me from the other side of the world to see whether she should call an ambulance for our father - the answer was "Yes". I expect if she'd called 111 they would have told her the same, but maybe not, and maybe there would have been hours of delay while they got a HCP to call back and check symptoms. (To be fair, I haven't used the system for years, so I don't know who answers now - it used to be screening call handlers who had a procedure to follow, including "I'll get a nurse to call you back" who then might say "I'll get a doctor to call you back" - hours)