Okay, let me try to explain, lol. I just got the dashboard update finally, so, ugh. Basically, graphic makers have been designing graphics for years to fix a 500px wide layout. This includes 500px wide gifs, and then gif sets with two gifs in a row being 245px each (to meet the 10px gap in the middle), and sets with three in a row being 160px each, etc etc.
Now, tumblr has changed the size of the main posts on the dash to be (I think) 540px. But instead of leaving old sets as is within that, they have coded it to stretch the gifs/pictures to fit the new size. When you take an image at one size and make it bigger, it doesn’t magically look good. It stretches, and it gets blurry. So, on the dashboard, a gif that actually looks like this:
Turns into this instead:
See how it’s bigger, blurrier, and the text is almost cut off a bit on the bottom? Yeah. That. For literally every gif set and graphic made in the years this site has been running. The still edits have also been stretched to fit, making them blurry as well.
And that’s not even taking into account how it has completely messed up personal layouts (mine, for example, looks like this), or how now, if this sticks, all graphic makers are gonna have to change the sizes they make their gifs (the thought of editing all my actions makes me groan), and bigger gifs means we can have less frames in them now, to meet the 2mb limit on gif size.