When I’m writing a post in Tumblr and it exceeds the length of the writing box, this happens:

I can’t extend the writing box, and am therefore crammed into this tiny space to write in. Forced to scroll up and down to refer to different parts of something I’m working on, I’m annoyed and unproductive.

If I’m writing the same post in WordPress and reach the end of the writing box:

I simply stretch it:

*edit* Daniel Wajda pointed out that when you’re in the HTML view, you can stretch the window to any size.

^ this is great, but users that want to do things the easiest way (which is probably why they’re using Tumblr in the first place), it’s not possible to do so. 

Most of the time I find myself writing in the “easy mode” as I don’t need the power or flexibility of the markdown editor.