Need Help Making Sense Of Cancels

As I sort through a collection of used stamps that I recently inherited, I have been coming across some cancels that I have not been able to find online. For example, the airmail stamp below. While I have seen the AIRMAIL SAVES TIME type cancels on ordinary postage stamps, I have yet to come across them on an airmail stamp. It seems kind of redundant to me, but I'm not the expert. So I come here: How common was it to do cancel an airmail stamp in this way?

Very common

Yours is better than average as the cancellation plane and words are well centered. A sock on nose if it was the date ring.

Great positioning even if the postmark is common, and an attractive item as a result

Very attractive stamp and cancel.

As others have mentioned, the slogan cancel is fairly common, however being well-centered and legible on this stamp has eye appeal.

The "air-mail saves time" PSA advertising slogan cancel was applied to any type of mail which might normally receive a machine cancel. Thus the slogan can appear on stamps for a variety of purposes, regular, airmail, special delivery, which get dropped in common letter boxes.These cancels have been well documented by city and range of dates. Here are some other airmail stamps with the slogan including the last one showing the later major variety with the monoplane.