When I grow photos I top. With autos, I don't. The reason is that topping requires recovery time. With photos, you have as much time as you need by extending veg. In other words...with autos, you're on the clock. I also find that stunting can happen with autos and it's almost 100% down to genetics, and not usually a function of skill level. When it works, the result is a nice-looking plant. I've tried it both ways and came to the conclusion that manipulating the light during early growth allows for an even canopy without the stress of topping. Even if I end up with a Christmas tree structure I still have 13 or 14 satellite buds that all combined has about the same yield as a topped auto...that didn't stunt.....but that stunting part is something you can't control, so why take the risk when there isn't much to be gained?
You don't need to touch an auto to end up with an even canopy.
I set the dimmer on the lowest setting when this plant was a seedling. I gradually increased the light as she grew. Doing this stopped her from being leggy. That is how to avoid ending up with a Christmas tree. The result was a plant that responded with an even canopy without doing any topping or training. She yielded close to 1/2 a LB of solid nugs. Mephisto Alien Vs Triangle F2.