Some subgroups have electric tools run by a generator outside the barn, others may have air powered tools and others may have a very old fashioned water wheel running belts to run the tools, it depends on the particular sect.
But yes the main reason it to be not dependent or connected to the outside world partly for self sufficiency and partly to keep out corruption
I fall somewhere in the middle, I'm connected to the outside world because there is good stuff to be found (such as this forum) but I don't follow the hollywood/pop culture or sports or non christian music, etc.