WhatsApp is testing a new feature secretly that allows texts to disappear from the sender and recipients' DM after a while.
The messages will self destruct after a set period which helps add an extra layer of privacy beyond messaging encryption.
Having an accumulation of your texts on different phones is a bad idea privacy-wise.
That is most likely why WhatsApp is testing out this new tool.
The feature is not publicly available yet though its existence has been verified.
According to reports too, the feature is not near perfect yet as there are still potential ways to go around it in order to read user texts without user approval.
Screenshots can be used to record messages remotely by a third party and that is hardly WhatsApps' fault
WhatsApp tests new features all the time but not all of them eventually get shipped, so there's every possiblity that this particular feature may not see the light of day
WhatsApp may conclude this new element is certifiably not a smart thought and scrap it so don't get excessively energized at this time.