When lambs are born they are extremely vulnerable to the elements, particularly wetness or wind. They can cool down very quickly, lose their mobility and not get that all important first suck of milk, and before you know it ... a year's effort wasted (for that ewe anyway).
A good mother will turn, get up and lick her lamb, gurgling and talking while she is licking. Licking stimulates blood flow and the talking stimulates a response from the lamb. The lamb will try to get up and reach the teats for a suck. Good mothers almost seem to encourage this!
The earlier lambs suck the better chance of survival they have. This is especially true with twins where there is a time the first lamb is on it's own while the ewe is having the second lamb. Good mothers don't ignore their first lamb during the process, continuing to talk and reach out to it while lambing the second lamb. However if the first lamb has already had a drink it's in good stead while waiting for it's sibling to be born.
Good mothers also stay close to their lambs and the place they lambed at for longer. There is research that shows this results in higher lamb survival. Ewes that talk to their lambs, stay close, and get them fed are less likely to lose sight of their lambs, or to have their lambs walk off in search of a mother.
So yes, absolutely, good mothering makes a big difference.