Well, the advice is aimed more at the beginner, and I am assuming the tree is a small sapling with little in the way of branches and foliage. Im really guessing without a photo.

You have to be careful of pruning too early with Pines and I think inexperienced growers can be too enthusiastic about pruning and go ahead during the nice warm summer months. Trouble is that books tend to advise snapping candles as they extend and I, for one, was inclined to do that on young trees before I knew better. If pruned too early before the needles have set then it can cause problems with needles continuing to elongate in order to replace their fallen brothers, which is something you don't want.
Also, one must bear in mind that many old needles will turn yellow and fall in the late summer and one must be careful not to prune into these areas which could leave you with no foliage on the branch, and it could die off.
Another advantage with leaving the pruning until later is that the stem should thicken up more in the later part of the summer.
The roots are active at this time also, but I tend to think that leaving more foliage helps the roots grow which will help the tree for next season.

When I say winter, its usually more like November, rather than late winter, but I find the back budding to be satisfactory.

That my thinking anyway, and I am no expert, but its an interesting subject..

You are right with regards to what an enthusiastic beginner might do - I'm champing at the bit to start cutting into my Scots Pine sapling!!!! Thanks to Paul's advice I've held off and will give it a good summer of water, food and sun. Since potting it into a bigger pot, it's already growing on well.

Following Nick's comments here, I may prune it in November and try and encourage some back budding as it's very leggy. Thanks for the discussion gents ......

Keeping a visual record of before and after helps you to evaluate what techniques and timing works for you