That way you can use a thinner shell and take advantage of the low fundamental tone. Most of the same ideas apply to toms, although the bearing edge is the most important factor for toms. A sharp edge gives the drum more attack, whereas a slightly rounded edge will give you a rounded, warmer sound, since more of the head comes in contact with the shell. Finally, the finish or covering applied to the shell is important. A lacquer finish will resonate and vibrate with the shell more freely than a plastic covering that is glued to the shell.
Plastic is excellent for durability and a lacquer finish requires more care.
Your choice of finishes really depends on personal preferences and price range.