It is important for two reasons… to keep it from rusting, and to prevent sticking.
I really don't find it a hassle. If I am cooking with oil, when I am done I just remove the bits, wipe the oil out really well (and go around the entire pan), and then set the oven for 425°F for two hours and put the pan in upside down.
If I am cooking with something other than oil, I'll rinse it out, put it on a med-low burner for a few minutes, then add a dash of oil and repeat the above.