Yeah, it's a good way to demo your brand/product before dropping a couple of million on your own brewery.

Friends who have opened breweries have said that having the product information from contract brewing as part of your business plan makes it much easier to get the business loan (if you're going with traditional funding, which has other downfalls)

https://www.peabodyheightsbrewery.com/co-op-brewers/

You brew on their equipment, with the help of their brewer, and under their license. But I believe you have to get your labels approved by the FDA yourself.