We did it for 4 years at our Alberta place. We calve from mid-May to July 1st, and we had the grass to ensure we were rotating cows throughout the fall to keep them gaining and in good shape going into winter. We were mostly grazing stockpiled native for the winters, in river hills, canyons and coulees where there was plenty of tree cover and certainly not the winds that Big Muddy or other folks get. When it dropped real cold we moved the girls closer to home onto paddocks filled with bales we had spaced out for bale grazing. One winter we also swath grazed them on an oat-barley mix.
This worked really well for the first 3 years. The winters were mild, meaning it hit -40 a few times, but didn't stay that way for more than a day or two. The cows lost some weight, but never got thin. The calves still gained over a pound a day on average and we weaned them mid-March to give the cows 2 months off before calving again. My Grandfathers both told me not to get to cocky about my system because one of these years I was going to get an old fashioned winter that would put a stop to it all. The 4th winter was that winter. 2-3 feet of snow on the level. We had most of the winter's feed in swath grazing, buried, and even the horses got tired of pawing through for it. The cows would follow them, waiting for the horses to open up swaths, but when horses rub the hair off the backs of their legs they just quit. We rented 4-wheel drive tractors with blades and cleared snow off of swaths and did all sorts of things to get through, including buying hay in the middle of winter at peak prices. Bottom line, that winter cost us more in feed and labor than the previous 3 combined. Our cows were rough by spring and calves didn't gain a thing.
So from a cost perspective it's a hit and miss in my opinion. It may work for some, not for others depending on your ranch and management resources. It does definitely have other benefits. The claims of heifers being better mothers and grazers has proven true in our herd. The girls that were on their Mommas for 10 months are the last ones to bawl for feed when the going gets tough, and when the first snow comes they drop their heads and eat it for water without hesitation.
It's no different than any other management change a person makes-you have to gauge the results and decide for yourself. If you want to stick with it there will be cows who don't do well and you have to decide to either feed them more or sell them. You have to look at possibly changing minerals or supplements depending on the feed value offered to the cows, etc, etc.
We've done it now for 6 years in total and this winter in a milder climate in BC I'm looking forward to seeing the results.