Most stylists prefer to cut hair that doesn't have hairspray, gel, mousse or other styling product in it, because they gum up their scissors and also makes it difficult to get a comb through the hair.
If the hair is long and tangled, that would be a problem.
If the hair is terribly oily, it is difficult to get a nice even cut because the scissors do not cut through the hair as well when there is a large amount of oil built up on the hair shaft.
Other than that, cutting it without washing is not a problem.
I usually wash my hair the day before cutting it, but it is perfectly fine to wash just before cutting. Most stylists are taught to wash the hair before cutting it.
If the hair is long and tangled, that would be a problem.
If the hair is terribly oily, it is difficult to get a nice even cut because the scissors do not cut through the hair as well when there is a large amount of oil built up on the hair shaft.
Other than that, cutting it without washing is not a problem.
I usually wash my hair the day before cutting it, but it is perfectly fine to wash just before cutting. Most stylists are taught to wash the hair before cutting it.