Normally I do not snorkel around the reef, rather I prefer donning full kit including tank and regulator allowing a more immersive experience. Staying down allows me a freedom of movement, to explore well beyond the twenty five feet or so that I can reach without the gear. Scuba permits me to carry a camera with time to compose a subject and observe behavior.
But on occasion I hit the water with minimal gear, simply mask and fins Sometimes I am accompanying a friend who is not a qualified diver. Perhaps there is no time or allowance for the large amount of gear scuba required and I simply want to swim. Snorkeling is nice this way, taking a long swim is hardly boring when so much is visible just below.
I skim along, the large fins providing effortless speed. The view is different than that of scuba, you are always looking down. I stay in the shallower water where the coral comes close to the surface. On occasion I dip down below the surface to get a closer look, weaving through the coral on long shallow dives. To go up I simply stop swimming to allow my buoyancy to lift me to the surface. A sharp breath clears the snorkel of water. With practice the actions are almost reflex, as natural as breathing on shore.
There are species that prefer the shallows, rarely seen when diving, often common in just a few feet of water. Snowflake morays, the colorful lagoon triggerfish, snorkeling allows spotting of a different reef community. I often make a point to sweep the areas just off the shore in three feet of water or less, just to see what can be found.