Requirement of EOG:
1. To reduce load on Loco to pull the Coach, as AC Coaches with Dynamo require high resistance to be pulled & hence Loco power gets utilized to negotiate friction, which affects both acceleration & MPS!!
2. With EOG, AC Capacity dont get affected if train has unusual or long stoppage, as power remains unaffected as compared to stored power in Dynamo (which reduces with time & if train has too much of stoppage or breaks, then AC isnt constant-as in Intercity)!!
3....
more... ICF Coaches especially for Rajdhani or complete AC Coach were designed with no Dynamo (for AC), which require EOG to cover the load factor!!
4. EOG was visible in Normal Mail/Express (Asr Mail), having high AC Coach count but limited Loco Power (earlier)!!