There are no set rules on this, though there are differing opinions. While including large pieces of cheese and knives for guests to cut their own pieces is easiest (and allows them to choose their portion size), it will likely lead to a messy board. In comparison, providing ready sliced cheese means equally portioned amounts that are easy to grab by guests. However, sliced cheese will dry out quicker (especially if you end up with any leftovers). For the best of both worlds, I recommend slicing the first 1/3-1/2 of your cheeses.