Crisp-crusted, with salty bits of crackling fat and a moist, pink, juicy interior, a boneless roasted leg of lamb is one of those spring treats that makes me wish winter came more than once a year just so we'd have more excuses to cook it. I'm not sure exactly when lamb became associated with Easter, but I'd like to thank the person who made it happen (it baffles me how little lamb we eat in this country compared to the Big Three meats).
While hard-core traditionalists and cooking show judges will chastise cooks who remove bones from roasts claiming that bones "add flavor" or "keep the meat moist," anyone who's done some A/B testing, owns a thermometer, and has a decent palate knows that this is mostly nonsense. Flavor doesn't penetrate particularly far in a piece of meat, and there is no significant exchange taking place between a bone and the meat immediately surrounding it.* A bone can slow cooking, helping you to nail a final temperature more easily, but having a good thermometer solves this issue handily.
*You can prove this by removing a bone, wrapping it in aluminum foil, then reattaching it to the meat. The cooking qualities and finished flavor between that roast and a fully intact bone-in roast will be indistinguishable.
The advantages of boneless lamb? Flavor, texture, and ease. Flavorwise, removing the bone means that you can then butterfly the meat, rubbing the interior with a flavor-packed rub, like this garlic, anchovy, rosemary, and lemon zest mix (don't worry, it doesn't taste fishy!). As far as texture goes, butterflying lets you trim out excess connective tissue, as well as salt the meat more deeply, which both tenderizes and helps retain moisture. An even shape after rolling also means more even (and therefore more tender) cooking. Finally, a boneless leg of lamb is much easier to carve—just rest, slice, and serve.
Read up a bit more in my Guide to Buying, Storing, and Cooking a Leg of Lamb, or my technique for Slow-Roasted Boneless Leg of Lamb With Garlic, Rosemary, and Lemon for more details.
Wanna know the best part about a good hunk of roasted lamb?