Tipping generally promotes a better result... ask any stripper.
LOL, outside there is no need to top. there is no need for a level canopy. If it helps expose a greater amount of leaf surface area to light, it's probably useful, but can also probably be accomplished without cutting bits off the plant.
unlike indoor lighting, there are no weak angles, corners or edges of a tent where light is 50% of what it is directly under the light. The plant is swimming in photons from all directions.
save yourself the effort. Just let it grow. Shape the plant a bit to spread it out as it grows. A trellis is good for support, but again.. an even canopy is wasted effort outside. Spreading it out is useful, though.
Plus, with autoflowers, it won't grow that large anyway.