Marketing of this kind is quite simply crap that does not mean anything to a ram client. On the contrary a ram client should be extremely wary of a breeder who claims this.
Firstly and most importantly, if you shepherd your ewes at lambing time, the primary reason you do this is to ensure that you (as far as humanly possible ) are recording the correct dam of the lamb and thereby also recording the correct sire of the lamb. Accuracy is important in assessing the genetic potential of any ram, without accuracy you can only go by the quantitative and qualitative data pertaing to the animal itself only. Without accuracy in the pedigree any SiL figures are basically a waste of time.
Secondly shepherding your ewes at lambing time, enables you to record other relevant issues, such as lambing problems (if any), milk production, good/bad udders, constitution of the ewe etc etc. Much of this will be not be visible at tailing time, when lots of other factors will be influencing what is going on. Anything that isn't good with the ewe or the lamb, you can record or mark and cull it, it doesn't have to die to not be bred from.