One of the most contentious topics in snorkeling is whether to snorkel from shore or a chartered boat. Many people have strong preference one way or the other; however, there are benefits to both methods. Shore snorkeling is the easiest and fastest way to get in the water. Because entry points are freely available, there is usually less chance of swimming in a big group, as you would on a guided boat snorkel. Shore snorkeling sites are usually minimal in cost--occasionally snorkelers will encounter marine park fees or beach entry fees, but often shore snorkeling is free! Shore snorkeling can be done any time there is enough light and anywhere snorkeling is allowed. Chartering a boat allows snorkelers to access sites that are too far to swim, which often are the "must-see" areas of many snorkeling destinations. Boat snorkeling is nearly effortless--snorkelers board the boat and jump in the water right above the snorkeling site, eliminating long swims. Between seasickness and group size limits, it would stand to reason that fewer people visit off-shore snorkeling sites than visit sites that are easily accessible from shore. Fewer people usually correlates to healthier reefs and a wider variety of marine life.
The best way to decide which method to use is weigh your personal preferences with the location of most snorkeling sites. Places like Bonaire and Curacao in the Netherlands Antilles are well-known for shore snorkeling sites, while many fantastic sites, like Molokini Crater in Hawaii, are only accessible by boat.