Pressure and hot gas flow erodes throats, not that an already hot barrel doesn’t compound the issue. If you’ve shot to the point you can’t comfortably hold the barrel in your hand and continue shooting, the barrel is suffering damage. Letting it stay in a warm/semi hot state during use is likely to cause the least damage. Mag dumps? A few quick 30rd mag changes without cooling is going to do noticeable damage. Need an oven mitt to hold on to the tube or it’s so hot you are afraid to case it and it on its way to becoming toast.
Note that the damage may not be all that apparent if you are not keeping track of accuracy from the start. If all you expect or desire from your rifle is the capability of hitting a 12” gong @100 yds you most likely won’t see much change Until the bullets start flying sideway. I changed out a barrel on a M70 HV .223 a few years back that had at least 8/9K rds down it and, had been boiling hot more then once. The throat was a checkerboard for the first 5” or more, but it would still hold 5 rounds around 1.25” or a bit less at 100 yds, but when new and for most of the time I shot it, it was a honest .5” rifle. The new barrel has it back shooting the little bug holes I expect from this type of rifle.