In as far as a life saver, the full wetsuit has saved many a life in colder water conditions. Even more recently, in March of 2009 a kayaker was stranded in the icy waters around Seattle. Thank goodness for well trained ferry personnel, city rescue personnel and onlookers who managed to rescue the errant kayaker. What actually happened was that the man involved had inadvertently overturned his kayak and ended up in the freezing cold water, luckily with a full wetsuit on, which enable him not to get hypothermia and literally freeze to death, whilst the ferry got close to him. The ferry, packed with passengers, had to return to the closest point on shore which was back in the direction that it had come from, nobody minded though in this heroic rescue attempt.
The outcome of the above event would have been completely different, had the kayaker not had his full wetsuit on, as well as the gallant efforts of the rescuers. The fact of the matter remains in this instance the wetsuit provided the life saving insulation and functionality for the kayaker, who had incidentally never had a capsizing incident such as this before.
Hence the necessity of the suit is proven in colder conditions, as well as by the many scuba divers who use the suit for protection from scratches and stings in the sea. This can be from the coral reefs, wreckages or the rocks that they dive in and around, and a nasty scratch is not something you really want in shark infested waters. The pain from a jellyfish or bluebottle sting is also enough to bring you out of the water fairly quickly, and this is where the neoprene material of the suit also provides this much needed protection in the water. This of course is over and above the insulation provided.
Considering the issue of necessity or luxury based on the functionality we have described above clearly points to the fact that the full wetsuit has many advantages and benefits to the user of this type of equipment. So necessity or luxury, you choose.