A definite pro for me is the ability to place my store on 'vacation mode'. If I'm going out of town for more than a couple of days, I turn on vacation mode and don't have to worry about ending 200+ individual listings.
You get a discount on fees. If you do enough volume that pays for the store. You also get a coupon for $25 every three months to buy store supplies. A basic store comes with 250 BIN listings & 250 auction listings. Extra listings are at a reduced rate.
Another plus is that you can list your items for 30 days rather than the usual 3-5-7 and you can also set them to automatically relist if the auction goes unsold. This saves tons of time if you're dealing with large volume.
It's my understanding that if you consistently list 70 or more items a month you should start considering a store. That's assuming you don't get free listings & that listings cost about 30 cents each. When I opened my store I was selling $1500/month minimum and the store fee was $15/month if you signed up for a year. At the time the discount was 1% of sales so I was at break even. As a bonus I could leave town for a few days & put my store on vacation. I was also guaranteed a set amount of free listings every month so I didn't have to wait & hope that eBay would send out an offer for free listings.