It's not essential. It allows you to sail dead downwind. But most
boats are faster on a broad reach, so while you cut the distance, any cut in time will be small.
They can also help in very light
wind, when the
wind might not be enough to keep the sail filled. Many people start the
motor on those days.
It takes significant practice and thought of setup to manage a pole singlehanded. I have it down to an art on my
boat, but it took several years and about 20,000 miles before i got it all worked out.