The reason a batter hits the plate with the bat is to make sure it has no hairline fractures, especially in the handle. From the time I was a tiny Little Leaguer in the 60s (still using wooden bats) until watching my nephew play semi-pro ball (with wooden bats), this was the general routine. Hitting the handle on the plate will yield a hollow sound and/or cause a visible crack to open. If the bat is loaded with cork or otherwise juiced, the batter tosses it back toward the dugout asap.
Measuring the distance of a swing is a different ritual. For that, you touch or tap the head of the bat on the inside of the plate. When you raise the bat to a vertical position, the head of the bat will reach just an inch or two past the outside part of the plate. Geometry in action!
And while I have seen batters check the bat by hitting the handle on the plate, I wouldn’t call that a ritual so much since they tend to only do it when they suspect the bat might be cracked.
Tapping the corner of the plate is more of a ritual and I suspect what the original question was about. Some players do like to tap both inside and outside - superstition beats geometry every day.