Rooting is great, where possible. Many cheaper devices though are still unrootable, usually because it hasn't been possible to build a version of TWRP for them.
Many non-cheap ones too, notably Samsung and LG (in the US).
If you want rooting and a bunch of storage, your non-cheap options get harshly limited. Looking for such a phone over the last few months, the options for my carrier were Motorola or bust. Which means getting an Edge, which are goofy and expensive and have defective screens.
So I gave up and got my first unrootable phone, from Samsung.
