lock-ons

You can certainly run just the one center rail lock-on.  The outer rails have the advantage of being two, plus being connected electrically to the metal ties.  If in the future you find some problem areas, you can always run wires to the outer rail connections.  

That said, personally, I would run both wires at the outset of layout building, if I was just starting a layout build.  

As Dan said you don't necessarily need to do everyone, but making lots of ground connections really helps, particularly with older tubular track where tarnish in the sockets that receive the pins can reduce the power. 

I build a lot of floor layouts with tubular.  The first wiring step is to run grounds to as many places as possible.  I don't just use lockons.  I use O22 switches and the center wire post is ground.  Connecting a ground there transmits power to three tracks. 

If you are running TMCC or DCS there may be special considerations.

 I have had very good results with consistent power throughout the layout.

Bill

I read your post from 12 / 22 / 19 about a ground wire to the center post on a 022 switch. Being a novice can you possibly explain or describe how’s that’s done from power to 022 switch. I run o gauge using KW transformer. 
Thank You

Rwmarkiewicz@gmail.com

Run a wire from the KW "U" terminal to the center/ middle terminal on the O22 switch motor. This provides an additional outside rail "ground" source.

You can also make both lockon connections at RCS / UCS tracks(or tap into the controller wires near the panel) if you want to cut down on lockons or reduce voltage drop around the layout.

In addition to the 022 center post for ground/common, you can use the fixed voltage jack for a center rail connection by using a DC coaxial plug instead of the original 711-151 and connecting the center to fixed voltage and the sleeve to track voltage.

thank you for the reply, greatly appreciated.