So how does this feature work? Basically it is designed to make the sending process more seamless and to cut down any waiting time. When you select the photo(s) that you want to upload, a copy is said to be sent to WhatsApp’s servers where it awaits confirmation that you want to send it.
Usually what happens is when you send a photo, you are brought to the editing screen first where you can crop it, add captions, doodle on it, and so on, but with this predicted upload feature, a copy is sent to WhatsApp’s servers in anticipation of you sending that file. The file remains on WhatsApp’s servers until you hit that “Send” button, which means if you decide not to send it, nothing will be sent.
At the moment it appears that this is only applicable to photos and videos and other files are not compatible with this feature for now. It is said to be rolling out to both iOS and Android users, but we have yet to see it on our end so maybe it will take some time before it reaches everyone.