There are some obvious drawbacks. You need a large freezer - something not common in the city. You also need to be comfortable with cutting up big and unfamiliar sections of butchered meat. Some butchers and farmers do cut up whole pigs or cow sides into more familiar cuts, but often you are committing to bits of meat that you've never cooked before.
The benefits, however, are also obvious. You can buy a pig, lamb, or beef cow from a farmer that you know and trust. You can know that the animal was raised well and slaughtered humanely. You also learn to eat "nose to tail," dealing with unfamiliar cuts and pieces of meat that often turn out to be delicious.
We have never had a freezer big enough to accommodate the pig, lamb, or cow that we hope to buy this winter. Hopefully by then we'll try out this form of meat shopping.
Have you done this, and if so, what was your experience?