I remember friends talking about jail breaking IPhones (3s and earlier) because jailbreaking allowed multitasking among other now basic features.
Now, the main advantage seems to be using cell data as a hotspot. But most unlimited data plans also include some hotspot data.
My plan does but my phone refuses to let me because it wants to go through a bunch of hoops to enable it.
Of course it also usually is either slower or pretty constrained (I think I get 3G tethering with my plan or could pay an extra $10 a month for I think 20GB of LTE tethering; I think Verizon and ATT are worse but I haven't checked their plans in some time).
So I think most people are just trying to get what they're already paying for.
Can someone explain the difference - Root vs Unlock* vs Jailbreak
* Not carrier unlock but unlock so that you can install 3rd part apps
Jailbreak I think was specific to Apple and referred to getting around their base OS security so you could run modified stuff. I'm not sure how that's changed over time.
Root is similar but often is done in order to install a more pure AOSP version of Android to bypass the OEM customizations (and carrier bloat) that many Android phones came saddled with. I think it used to be necessary in order to install different launchers and do some other things that now doesn't need root access. But there's still other things that do.
Unlock is simple. I think any Android phone can "sideload" apps (which is installing apps from a source other than the Google Play Store) without root. Well its a bit more complicated in that Amazon's phones (which run a version of Android that Amazon customized), wherein you have to sideload to install normal Android apps on them. I think you have to jailbreak in order to do that on iPhone (although I believe there was one exception, and that was enterprise - large corporations - could manage things which let them adjust different aspects, which I think they lock things down more so I'm not sure it would be useful for bypassing the stuff that people are jailbreaking for; I also think Apple might've clamped down on that some as they found out that some malware was using some of those enterprise software flags to bypass some of the security features and infect phones).