Some of railways coaches coupled with screw coupling(ICF) and some Railway coaches coupled with CBC coupling (LHB). Here are two pictures of CBC and screw couplings. 1st CBC 2nd Screw coupling.
When the train stop, there is little slackness between two couplings of coaches. At the time of train starting, all the couplings stretch as Locomotive pulls the train. We Loco Pilots are advised to make a slow start from loco with small tractive force.
It gives them time to stretch them all couplings from front to end. Thus the train gets a smooth start. In screw coupling, the slackness is more than LHB coaches for CBC coupling. But in ICF coaches, additional protection buffers. Buffers absorb the jerks. But as CBC coupling has less space inside between two consecutive couplings than screw coupling, LHB coaches can be started more smoothly than screw coupling fitted ICF coaches. Lastly, it depends on Loco Pilot how gently he could begin to his train.