I'm no Gasman or Milli, but I like to do a bit of engineering in TF2.
But I'm quite terrible in building my stuff when every few seconds an enemy soldier or pyro comes by and destroys the stuff I have just built because I'm running around collecting metal and I can't get it up quickly enough (bait for Nineblade).
So if you think a sentry, dispenser or teleporter would be a nice thing to have around and you see that the engy in question is not a superior warrior it might be a nice if you'd hang around for a few moments until the buildings are up (at least to some degree).
In other words: Help me to help you

I agree with this... Especially when on the attacking team, everyone keeps pushing forward past yourself, dying and leaving you wide open.... and then when the spawn they ask 'Where the hell are the teleporters?'
So bloody frustrating.
Classic point for this is attacking in goldrush stage 1 cap 2, upstairs on left (from attackers view) is perfect place to get a nest going but no-one hangs roud to protect an engi up there.