So I added a bunch of images to an email and hit "Send". Gmail is still uploading them, but I do not and should not care: do what you gotta do and send the letter.
But instead Gmail gives me a non-choice: send the letter without attachments (why would I say yes?) or cancel sending altogether (why would I say yes?!).
In other words, I have to wait for the machine and click the button when the machine is done. The machine is being the user, and I am being the servant.
What makes things even worse is that there is no progress indication of any sort. If you have a bunch of images drag'n'dropped into the body, they just start uploading asynchronously in no particular order. You have to scroll up and down to see if it's done or not.
Of course, the only sane way to manage this use case is to give me at least one option that correspond with my intention: "send after upload is complete".