Ventajas
There wasn't an option for the location I worked at here on Glassdoor so I guess all reviews go to this corporate page. I worked for 2 different franchise locations over the span of ~12 years. During that time I worked with AGI (the corporate HQ) many times. Really good people. But I'll be focusing on working for a franchisee. Some pros: Work with a variety of clients with different styles and needs. Every day brings new challenges and opportunities. Great way to quickly build a portfolio of work that doesn't just focus on one company.
Desventajas
The company name is not as "prestigious" as other creative jobs. It's a franchise so each location is independently owned and operated so each owner is a bit different and runs their company differently. Depending on the size of your team you may not be doing creative work all day. Also benefits can vary from location to location. Some owners value creative work more than others. I've seen locations that treat creative work as a necessary evil and don't make much money if any at all on design work. Others view it as a profit center and really sell the design work to clients. You want to work for a location that does the latter, but make sure you have the skills to back it up so your team feels confident selling your creative work.