I was "lost at sea" for a few hours in 30 kt winds and whitecaps and 8-10 ft waves last winter I think it was. (We really wanted to dive that day). After completing my deco, I wanted to save air so that if a ship tried to run me down, I could dive under it. Saw a freighter pass by inshore of me pretty close that day. Waves were breaking over my head and there was no way I could keep an eye on the sharks without a snorkel. You keep you BC full or nearly full, you keep yout face down and the snorkel points up. If it is not raising your "air acquistion point" a lot, then you are "doing it wrong"?
The waves still crash over your head (and snorkel) , but with a slow deliberate breathing pattern, you just inhale slowly when you can and exhale and clear the snorkel when you have to. If I didn't have a snorkel that day, i would have been in pretty rough shape after two hours of getting hammered. I was actually floating out there thinking about all the people on SB who say they don't need a snorkel. I hardly ever dive without one.
Also, this may pertain directly to your question; I hate all the mechanical snorkel holders, they allow the snorkel to move too much and are not comfortable. I cut a figure 8 out of heavy truck inner tube and make a DIY snokel holder that holds the snorkel very securely. It takes a concerted effort to spin the snorkel and it never slides down. It keeps the snorkel sticking up.