I jailbroke every iPhone I had for many, many years. Most of the time it was silly skins/tweaks but there were a number of things that were huge QoL improvements. I remember BiteSMS and using it as a way to reply to a text directly in the notification instead of having to leave the app. This was before iOS had that feature and before multitasking, back when if you left the game you were playing the app would quit. Also had folders before stock iOS, things like Control Center, and a whole slew of little tweaks for other apps I used.

The downside to jailbreaking was often the instability but that was also back when the phones were way less powerful. Today, armed with LLMs, I would love to have root on my iPhone again. I'd love to rip out Siri and replace it with Claude Code or something like that.