• Put an extra column of icons per page on my homescreen.
• Rename apps on the homescreen, and change their icons.
• Enable the iPad's "grid" app switcher on my phone.
• Remove the stupid app bar in Messages.
• Hide various UI elements around the OS and in apps, to make everything cleaner. (Cool note: you can use PermaFlex to hide nearly any arbitrary element.)
• Downgrade apps that release updates I dislike.
• Stop Apple News from creating "personalized" recommendations that would keep me in a filter bubble.
• Play audio from Youtube videos (in Safari) while the screen is locked.
• Install a Userscript that gets rid of AMP in Google search results.
I realize a lot of these things are nitpicks—some maybe even personal eccentricities—but taken together they just make my phone a lot more pleasant to use. I would not buy an iPhone I could not Jailbreak, full stop.