What is the difference between a coastal cruising and blue water sailboat?

The designs, accommodations and compromises for these boats can be very different and reflect the likely sea conditions these boats would encounter, expected time at sea and different experiences of passenger comfort.  The primary difference between these boats begins with the shape of the hull since many other design choices tend to be dictated by hull shape.

Coastal cruisers, which are generally sailed near shore and in safer weather conditions, 
tend to have a flatter hull shapes since these boats, which means they tend to "slap" the water when coming off a wave.  With a flatter hull shape, boat architects can make greater use of the cabin space and so coastal cruisers will generally have a more spacious interior.  The helm (or the outdoor area from which the boat is navigated) is generally less protected and generally speaking, offers greater comfort and ease of moving around.  Safety, protection and expected time away from marinas mean these boats can refill fresh water, recharge batteries, empty waste tanks more frequently and therefore, tend to have lower capacities.

Blue water boats, because they are intended to sail in open waters (hence the moniker "blue water") in more unpredictable weather, generally have tapered (or tear drop shaped) hull shapes with heavier keels (generally, lead) and deeper drafts.  With these designs, blue water boats can withstand heavier seas and will "cut through" waves rather than "slap."  Generally speaking, blue water boats offer a much more comfortable experience in rougher seas and will have bigger fresh water and fuel tanks and will likely feature generators and other equipment that allows these boats to away for longer periods.

Blue water boats feature tapered hulls so the beam or width of the boat narrows the closer it gets to the water line (and below), leaving less room in the interior cabin than an equally sized coastal cruiser.  Foot for foot, blue water boats will feature fewer berths and will have more cramped quarters because of the narrowing beam.

Because blue water boats are intended to sail longer distances and will carry more fuel and fresh water, these boats interior space is further restricted to accomadate these practical requirements.

The differences in comfort, stability and likelihood of capsizing are all captured in mathematical calculations that can provide an abstracted comparison between these boat types so prospective buyers can anticipate the the experiences and trade offs each hull type would provide.