When we released Apollo, we didn't really know how many files our users would upload (having a completely oversized hard drive ended up being a really good idea!). As it turned out, file attachments were (and are) a huge part of many Apollo workspaces.
This is why we felt it was important to improve the uploader so that:
It wasn't "blocking": this means that you had to be able to write your message while uploading your file
It worked with drag&drop: Google does it, modern applications do it, and users are expecting it more and more
So, we updated the file uploader in order to cover all of this ground:
With this update, you can drag a file from your computer over any form in Apollo that takes file attachments: the file will begin to upload, and you will be able to write your message at the same time.