Gears are great, but a simple single speed set up makes rides more interesting and you a lot stronger and better rider.
I recently converted my Niner ROS 9 Plus from a geared 1x11 speed set up to single speed. Some frames are built with the ability to run a single gear in mind using either adjustable/sliding drop outs or an eccentric bottom bracket. Niner has gone the eccentric bb route and it works flawlessly.
Single speed isn't for every trail or rider, but it will help anyone get faster and stronger on the trail.