I planned a long weekend in Paris over MLK weekend and see it's the time of year for the winter sales. It's hard for me to grasp bi-annual sales periods since in the US there's some kind of sale every day! What's it like? Are the sale prices worth it? Is it primarily designer stores? I like to shop but doubt I'd plan a whole weekend to it. Frankly have made no plans at all and I'm mostly looking forward to eating fabulous cheese again!
there are laws limiting sales during the year so these big sales are the real deal. For example when my grandchild was a baby I shopped for high end baby clothes at Galleries Lafayette; I found several cute things but they were really pricey so I was trying to decide which one to get. I went back the next week and they were half price -- so I got both things I had been looking at.
They seem to be selling real merchandise that is sold during the year not just 'sale merchandise' trotted out for the sales.
There are kind of two different philosophies: There are those who line up outside the stores the morning the sales start (January 6 for this next round) to get the prime items the minute the shop opens (many of these people will have spent time in the stores in the days prior, trying on clothes or in general scoping out what they believe might be put on sale, so they're ready to POUNCE and get that deal!).
Then there are the folks who wait for the second and third "démarques" or discounts, which sounds like what you'll be there for. For example, on the first day of the sales, the item has a certain percent off. Then at the second démarque (maybe a week or 10 days later, depending on the store), they discount it more deeply. The third démarque (again another few days later) more deeply again. So the question is: does one buy it earlier while it's still there, but possibly more expensive than it will be later, or does one hope for a deeper discount but run the risk that someone will have bought the item you want before it ever gets that deeper discount.
For you visiting it will just be fun to see what there is. The sales are EVERYwhere, from Hermes on down. Basically anyone is crazy to buy anything between now and January 5th, because on January 6th, so many things will be discounted (not everything obviously).
One other note: the sales periods are one of the few weekends of the year (aside from pre-Christmas) that some of the big stores are open on Sundays as well as Saturdays. This is usually only the first weekend of the sales, though, so I don't think it will be when you're here. But it's worth checking out the websites of Printemps, Galeries Lafayette, and Bon Marché to see if perhaps they'll be open.