I see a few things to be gained. First, if the intent is at some point to charter, then it's a plus to class up front. Second, mild savings perhaps on insurance. Third, it a new build it gives a very clear accept/reject level. If the contract calls for classification as a requirement, then it must pass before delivery...in theory. The problem is I've seen contracts that required it, the boat didn't pass, the builder had the money, still insisted on delivery, the buyer took it and ended up suing and won. (Marlow-Kakawi) Certainly that it didn't pass class as required in the contract and in all the builder's advertisements was a strong factor in the judgement.
I'm personally not familiar with a 50' being classed. However, it is my understanding that certain flag states require any vessel to be classed. Built to ABS standards as a requirement, would still give your surveyor something to hold to, if you had a surveyor who did class surveys and we went through all the steps. However, as pointed out above, it means nothing if just a builder's representation and not being verified by a class surveyor. Which brings us to what we consider most important, survey of a new boat. That starts with the start of the build however, in my mind, not just completion. It's periodic and regular inspections of the entire process, your representative during construction, to protect your interests. Class standards also include some things not included in ordinary surveys. Perhaps stability, deadweight and inclining, is the most important. Think Northern Marine and Baden.
There are many classification societies. The only three I have direct knowledge of are ABS, Lloyd's and Bureau Veritas. I am familiar with many boats also RINA classed as they're the Italian organization. The others are China, Det Norske Veritas, Germanischer Lloyd, Korea, India, Nippon, and Russia. Those you see primarily in their countries. There are another 40 classification societies but they aren't part of IACS.
With a larger boat the insurer is going to require a fairly extensive survey anyway, so the amount classification adds to the cost isn't as great. Classification was started by the insurance industry, as people like Lloyd's realized they didn't know enough to decide whether to insure or not. SOLAS also has recognized the role of Class.
I think classification becomes more important to a recreational boater when it's a custom build or even a semi-custom or when it's a new model in a production builder's line.
Also, when getting a surveyor for a new boat build, the fact it is a surveyor whose work the Class society accepts on a regular basis I think is a positive. There are a lot of surveyors experienced at purchase surveys and insurance surveys of completed boats but lacking experience in new builds.
Ultimately on a new build then, I'd want a Class Qualified Surveyor doing the survey and going through all the class steps. If I'm going to do that, I might as well go on and get it classed.
Also, note the word classification. That means suitability for particular classes of use. It's not simply one standard. It's determining if the boat is suitable for the class of use.
