Why does my English muffins package say to use a fork or fingers instead of a knife to open them?
If you cut it with a knife, you'll tend to get a very smooth surface. If you tear it open, whether by hand or with the aid of a fork, it'll tend to break on more natural places in the crumb, giving a bit rougher surface. When toasted, that tends to result in more contrast of texture - the bits sticking up will brown more and get crunchier.