Midi tracks are too recieve midi to record it and we echo so that it will go to the synthe of soft synthe yet when I have softsynthes some will continue to receive midi data when echo is off.  Global is channel 1
 
Keyboard --> Midi ( Track and midi input channel 1) (echo off) show activity and play GS STRUM 1 have to turn volume down for no out put
Keyboard --> Midi ( Track and midi input channel 2) (echo off) show no activity and does not play GS STRUM 2 do not have to turn volume down for no out put
Also I would think it would also be a good idea if a track is active in the console slot that it would change to the  color red to show that it is triggering or recording

Input echo will allow you to hear live input of an instrument - so with a synth, it will allow you to hear the output of a synth as you play it on a midi keyboard. Once the midi has been recorded in Sonar, the synth will play that midi data if echo is off. If echo is on the synth will still play recorded midi but will also respond to midi data coming in from your midi keyboard.
 
It is easier to understand Input echo in terms of recording a mic/line audio input rather than a synth. With echo turned off you would not hear a mic signal unless recording. Once recorded you would hear the resulting recording. But say you wanted to practice your vocals before you record - you want to hear the mic without recording. So to do that you turn on input echo. Now you can hear your voice for setting levels, rehearsing etc. It's the same with midi instruments - echo allows you to hear the sound without recording.