I agree trying to sell in a retail store is very boring and repetitive, I've moved away from having one for my Sims to 'sell' anything. However, they do have one sometimes as a 'tax shelter' to reduce their bills. I guess a lot of Simmers like high bills though. *shrugs*
It's also possible to sell stuff in a retail store without any interaction with customers at all if you just use the Lice Cold Retail Freezer to sell home cooked meals, baked goods and produce. Customers just take out what they want to buy and your Sim automatically gets paid. They could open the shop and take a nap or do whatever while making a profit! I've had a shop like that which was very lucrative!
As others have said, another plus for retail shops is for immersion purposes and you can't sell furniture or other large objects using a yard sale table. There's the street gallery for paintings, but I'd rather sell those in a retail shop/art gallery, IF they don't just sell them outright or use Plopsy instead.
I mostly just use the yard sale table myself these days as well though, especially my Rags to Riches Sims. It's quick and easy, no actual interaction with customers required, unless you want them to, but it slows down sales. The only annoying thing about selling using the yard sale table for me is the need to constantly cancel customers trying to chat up my Sim! Gah! My Sim is here to sell stuff not gossip or chat about the weather! :D
Which reminds me about another factor against retail stores. Klepto Sims will steal your stuff! They can't do that with a yard sale table. That is, unless you've forgotten to lock the doors on their house. They WILL go in there and use your stuff or steal it unless you do. ;)
EDIT: I just thought of one more plus for yard sale tables. They can double as a fridge for Sims when they can't afford to buy one right away.