Masks are typically much lower volume than dive masks, more similar to swim goggles. Fins are much longer than dive fins, and monofins, where both feet are in the same fin, are sometimes used. Unlike snorkeling and skin diving, the main goal is to spend as much time underwater as possible. And time in the surface is only meant to re-oxygenate the body between dives. A snorkel is often not used. In very much layman’s terms, you could say that snorkeling is surface only, free diving strives to underwater only (or at least as much as possible), while skin diving mix the two. Participants in all three activities may not like this definition, but it can help others distinguish between them.
Also, a number of marine animals are easier to see and get close to when we don’t exhale bubbles, including whale sharks and dolphins. When traveling, it allows us to take a look below the waterline without having to bring or rent a lot of gear. For rescue scenarios, we don’t always have the
luxury of dive gear and may need to assist a diver using only our fins, mask and snorkel. Snorkeling is very useful when taking non-divers out to experience the underwater world.