1.) A snorkel allows face-down swimming without having to use your regulator.
2.) A snorkel effectively raises your airway by several inches, without having to use your regulator. This
can be helpful in certain wind/sea conditions.
(I) 1 and 2 above can be compensated for by most divers on most dives, so they don't miss their snorkels.
(II) Many divers have limited experience with proper use of a snorkel, do not position it properly, and compound the problem with the use of "foofy" modern snorkels with purges and gimicks that do little to improve on the basic "J" snorkel, and often are
worse than the old-stylde snorkels because they are harder to position properly and are less streamlined.
For an example of a "foofy" snorkel, see the one in my avatar picture. It cannot be positioned properly due to an integrated snorkel-keeper, and is too big. I used it for a couple dives, and went back to my 70's vintage plain-Jane "J" snorkel.
Most divers are fine and dandy without a snorkel.
Some of us have used them for many years, find them useful, and do not find them a problem.... the vast majority of my dives have been
with snorkel. I find it useful, but others do not.
Each diver gets to choose for themselves; I'm always amused at how heated the "snorkel debate" gets sometimes.
FYI: I dive open water, long-hose (5'),
with snorkel. You just need to rig and position the snorkel properly, and be slightly more aware depolying the hose.
Yes, I am a stroke
Best wishes.