Heavier bone has more surface area for the attachment of muscle. Heavier boned animals tend to be heavier muscled and more growthy, but it comes with a price, birthweights will drastically increase with heavier boned animals and higher incidence of dystocia will result partly form the bigger BW and partly because the thicker legs and bigger skeletal structure of heavier boned calves.
Note that the amount of bone is usually specified in the breed standards of most breeds, herefords for instance is a medium boned breed and light boned animals and extremely heavy boned animals are about equally undesirable in the hereford breed.
For the showring the heavier boned animals within a given breed standard is prefered, but be cautious when using a heavy boned bull, especially on heifers.
Pretty general statement. The heaviest muscled breeds of cattle also have the finest bone; Limousin, Blonde d'Aquitaine, Piedmontese, Belgian Blue. I think that the heavier bone plays tricks with our eyes a lot of times and just makes us think that the cattle are heavier muscled; that's why the show ring likes bone. Although we do have Angus cattle and the finer boned ones do seem to have less muscle; maybe your rule would apply within breeds, but certainly not accross breeds.
Knersie's post is an excellent example of the kind of answers which I think should be stressed on these threads. It explains why the bone size is important, and at the same time opens up the justification of THINKING about one's cattle business in a reasonable and sensible manner. People in the beef business can dabble in it as a hobby, they can use it as a supplementary income to another source of financial revenue, or they can engage in beef production as a full time business, either in a Terminal operation, a cow/calf enterprise, or as a Purebred protocol -BUT the critical lesson to be learned in this small facet of beef cattle management is that even the seemingly small details of analysis of an animal carries with it the important factors which may determine if a breeder will "make" it in the business, or "fail" to make a success of their efforts, even if they are just "playing" with pets.
Understanding how a beef animal is made and how it functions is important - even if one is playing with genetics. It isn't a game to be taken lightly. We are dealing with one of God's finest creatures! Thank you Knersie for a great answer to a sensible question!