How big is to big?

With the size of some yachts reaching pretty amazing levels, I've been wondering, how big can you go and still remain practical?

It would appear to me that some of the larger yachts are already pushing the limits.

Lets say you wanted to use this yacht for just about anything, exploring reefs (you'll want a shallow draft), staying in harbors, usually with limited or nonexistent facilities for really big yachts (less length and width means more available parking spots), and of course ocean crossings (the opposite of the others, you'll want everything as large as possible )

Is width as much as a problem a length?

What length, width, draft would you choose (from a practical point of view, not money)?