Yes, the Amputator taunt is useful. You can use the Medi Gun to heal people individually and get your ÜberCharge up, but you can save a lot of people's lives with the Amputator taunt.
For example, if a Pyro charges at a group that you are healing one-by-one and burns a lot of them, you might not be able to extinguish everyone before they die. The Amputator taunt will help in this scenario by quickly extinguishing all your teammates at once leaving no one behind.
I personally love the Amputator because it helps a lot of people especially when there are a lot of needy people who want you all to themselves. Using the Amputator taunt you can share the love.
You can read more about the taunt here.
Here's a quick comparison of healing methods:
Heals* Healee Duration Charges**
Oktoberfest 11 Self 4 s 0
Medicating Melody 25 Team 4.2s 0
(if in sight and range)
Medigun 24/s Target - 2.5 %/s
Kritzkrieg 24/s Target - 3.13%/s
QuickFix (beta) 36/s Target - 3.75%/s
* 300% for targets that haven't received damage in the last 3 seconds
** 50% for targets that are at 142.5% health or higher
Yukon was intentionally designed to be harder for Engineers:
This abandoned mountaintop coalmine was repurposed by shadowy operatives into a top secret surveillance outpost—one which also, so nobody gets wise, insidiously continues to mine coal. There is also a log hanging in the center of the map—possibly as an example to other logs. Logs that said too much.
Five control points promise a lot of momentum swings in this compact outdoor map, with plenty of tunnels and rocky outcroppings. Plenty of alternate routes ensure that if you can’t get past a well-placed engineer through one tunnel, you might be able to sneak up behind them through another.
CP_Yukon is a community map from the brilliant dual-powered brain trust of Patrick “MangyCarface” Mulholland and Joachim “Acegikmo” Holmér.
-- Classless Update, Day 3
Point 1
Point 1 is extremely poor for defending as Engineer.
If you're building full size sentries, it may be better to build them down in the pit, although that means a Spy can back-cap the point.
Point 2
Point 2 has a few defense spots. One of the best for actually covering the point is at your team's end of the hall when you first come out the door from point 1. You had better have the Wrangler, though, or a sniper at the far end of the can easily take you out.
Another point is past point 2, on the middle route. You can place a sentry on the walkway up. The problem is that, if you place is close enough to the point to be able to see it, it's far enough from the point 3 area for Demomen to be able to take it out.
Point 3
Thanks to point 3 being moved, your best bet is near the point itself, preferably where the fence covers it, so it can't be shot by Snipers (or at least where you can't be shot by Snipers). Your biggest problem here is people sneaking up behind you. You could place it at the very end of the point 3 bridge, facing the point to help counteract that.
Point 4
Building slightly to the enemy's side of point 4 works pretty well, as it covers both entrances to the point 4 area.
Another Alternative
Due to the difficultly in guarding points with a level 3 gun on this map, Mini-sentries work fairly well on it, at least when combined with the Frontier Justice.
Best Answer
Source: Community Wiki page