I have heard about people aligning their broadheads with their fletching. What is the purpose of this? How is it done?

IMO it doesn't matter if they line up with your fletching but it seems to help me if I put them all on the same. I'v got one bow I shoot with a release & broadheads fly closer to field points for me if I put them on with one blade right on top. My other bow I shoot with fingers & install them with a blade straight out on the left side to get clearence from the riser. Thats with 3 blade heads, If your using 2 or 4 blades I think it would still pay to put them all on the same.

http://www.broadheadtests.com/FAQ.html
It really makes no difference. The keys are proper alignment, good helical fletch, straight arrows and nocks and a well tuned bow.

No diff...
As long as they are striaght and spin true.
I do all mine the same way just to be safe.
(they look cooler that way too. almost like the arrow makeer knew what he was doing)

If I used a 2-blade, I'd have it horizontal so it couldn't blow off my rest as easy.
If you shoot instinct, you might also want a 2-blade horizontal for an easier to see visual reference point.

I agree. But I still align my broadheads with my fletchings, just like
them all the same. Guess it's just a mental thing.