the benefit to the B&M is that they develop a stronger brand. The benefits to the seller are the wholesale orders, which are often much larger and more regular than sales they would do on their own.
Private label is very common -- if you've ever gone to Target and seen "Target" brand toilet paper, shampoo, laundry det., etc., that is private label. Target doesn't make all that stuff. They wholesale from Charmin, Dove, Tide, whoever to sell them a version that they can put their brand on. They do it as a way to offer the consumer another option. The difference is that Target will have all brands on their shelves -- whereas your boutique wants only "their" items in their store, even if that includes ones *you* made. It's a way of offering their customers a wider variety, without watering down the brand they've built.
If you are more interested in building your brand and selling to the public, then wholesale may not be the right direction for you at this point. But remember that wholesale orders are typically larger in volume, and they will often become repeat customers -- maybe 4 to 8 times per year. So it can definitely be worth considering.
