I bought my 3 (standard) after the Pro 4 had been announced and agonized over the decision. I had have a great home work station and a really nice desktop workstation at home with dual monitors, plenty of ram, etc. I owned a Mac Air (2011) and an iPad 3 LTE. I'm a lawyer and wanted a single light weight device I could take to court/conferences/meetings to take notes, bang out simple word processing documents in court, occasionally present a simple PowerPoint, use on an airplane, and which could double duty as a tablet. I like the fact that the device was USB chargeable because it meant that I had more charging options. I immediately purchased an Anker ten foot braided USB charging cable to get a little more room when hunting for power.
With respect to the tablet competitors, I strongly considered the new iPad Pro and Surface Pro 4. I rejected both of them for different reasons. I agonized over this decision harder than I do in buying a new car and probably at the level of changing jobs. The larger faster machine has a lot of appeal, but it is on the days that go off schedule that having a companion device is great.