Is it normal practice to use 25 degrees of flaps when taking off at max weight in a PA-28-181? I recently started renting a plane (PA-28-181) from a new flight school and had to get checked out before I had the "OK" to rent. 

I had brought 2 family members with me during my checkout because...


They wanted to experience a small plane for the first time 
My intentions with the plane were to have the option to fly with a full load of passengers (which I couldn't do in the planes I was used to flying) so I wanted to experience what flying at max gross weight was like.


During the checkout, while in the runup area going through my checklist, the instructor encouraged me to go back through my checklist. Eventually after hearing this suggestion multiple times and not understanding what he was hinting to, he came out and said "You need to set your flaps to 2 notches because we're at max weight". 

I hadn't heard this before and I'm not seeing a ton of discussions about this type of thing online. His point was, the flaps would increase lift since we're heavy - that makes sense to me... But they also increase drag.

Note: this was not a short-field takeoff. 5,503ft paved runway, although it was hot (90+ degrees fahrenheit).

So, this leaves me with 3 questions:


Is this correct? When you're on the "heavy" end of the spectrum, should you be deploying flaps?
If so, what would be the proper flap setting at max gross weight?
Since, in this case, the point wasn't to clear an obstacle, would you simply climb out at Vy instead of Vx?
The PA-28-181 POH I have read says to set first stage of flap (10 degrees) for a normal takeoff, and 2 stages (25 degrees) for a short or soft field takeoff. I've flown PA-28s quite a bit and I've never heard any suggestion of using 25 degrees for a normal takeoff. At maximum weight on a hot day at sea level 5,503ft should be plenty at 10 degrees, even if you are at 4000 ft pressure altitude it should still be sufficient, so I see no reason to set 25 degrees. 

Setting 25 degrees for takeoff increases lift at the cost of drag, and risk as you are closer to performance limits. An engine failure on takeoff with 25 degrees of flap will give you less time to get the nose down, and stall characteristics are harsher with more flap. 

If the runway was shorter I would see 25 degrees as good advice. There are plenty of light aircraft pilots who don't do performance calculations before they fly, drilling 25 degrees of flap when heavy into them may just save their bacon on a hot day on a short airfield.