Bob, I have a lot of Legacy switchers (about 20) with electrocouplers but I still have uncouplers in the yard tracks, sidings and some mainline locations so I can uncouple cars in addition to cut off engines. Most S scale operators that use DCC also use Kadee couplers which require magnets in the track. Since I use Legacy rather than DCC I did not choose Kadee couplers. I basically have an uncoupler where I would otherwise have a magnet.
Only three rail O gauge offers a wide selection of switch engines with electrocouplers. Even then, to do other than cut off an engine, uncouplers are necessary.
Here is a picture of part of my freight yard. Five of the 11 total yard uncouplers are visible in the picture. In addition I have uncouplers elsewhere like this one pictured in Mainline 1 near the yard entrance. Just to the left of the uncoupler is a Sensor Track for the engines to communicate status with the Legacy system.