Since I prefer to do most surface swims on my back, I need a snorkel for 2 reasons: Florida Keys boats that require them, and the (hopefully-never-to-happen) situation where I need to hang out on the surface in high seas after a dive.
While checking in with a Florida Keys boat operator he asked to see my snorkel. I went over to the wall of his shop and grabbed a tiny pink kids snorkel with purge valve that fit into my BC. After trying it out, I realized that it actually was pretty good solution although about 3" shorter than a normal snorkel. I later added about 8" of tube from a 2nd snorkel which clips onto the first using a chopped up chunk of the 2nd snorkel mouthpiece tube. A rubber band from an old disposable underwater camera holds the snorkel in place on my head ( I tried the "slip it under the mask strap" method, but that tends to break the seal on my mask.)
The small bore offsets the increase in dead air space created by the extra long length.
Worked well snorkeling in 6+' seas off of Marathon a few months ago.
The tiny pink snorkel is good for a laugh when someone asks if I have a snorkel.
Clearly, YMMV in this case.