Its not a mistake, just a choice.
If you aren't going to be running prolonged high RPMS/racing its not that big a deal.
It helps keep the "free floating"
oil in the lower
oil pan area concentrated in the pan by subduing splash and frothing.
I did it on my initial build as I already had the engine torn down and it was just another little bit of insurance and yet another place to spend money on the beast.