Hi
Yes it is necessary as the high and changing amonia and nitrite levels can poisen your fish, and even if they can survive it you are almost certainly decreasing their life span.
I added fish flakes at the same time everyday for three weeks and tested water everyother day. As soon as the amonia and then the nitrite have spiked and returned to zero you can add your fish.
Fishless cycling is the best start you can give your fish, they are less likely to get ill in the future.
Good luck and be patient