On top of people mentioning text, I'll add chat emotes to the discussion. If you use anything like Twitch chat, it's filled with custom emotes you've never seen before. I can read text without each character having an abundance of pixels. Similarly sized icons turn to blobs at that size. High DPI makes those icons very clear even when tiny. I notice a huge difference between my 1080p monitor, my phone, and retina mbp.