Pros
I have been with Paylocity for 3 years and still get the new hire butterflies when I walk in the door. Paylocity hits all the staples for a tech company environment (open seating, game rooms, meditation rooms, on-site gym and cafeteria, yoga lessons, happy hours, paid parental leave...the list is nearly endless), but the thing that makes it feel like a tech start-up is the small company feel with 3,000 of my closest friends. I have continued to be challenged, given stretch opportunities, continuing education and the chance to collaborate across departments. Everyone has an opportunity to bring a great idea to the table that can have a direct impact on the product and the clients. Oh and it's okay if your idea wasn't that great either, failure is encouraged to be learned from. If you are looking for a company you can grow with and continued to be challenged for the long haul this is the place for you.
Cons
Not a con for me personally, but if working in a high growth high change environment stresses you out then this isn't the right fit for you. Change is pretty constant, but it breeds amazing opportunities for growth and learning if you are up for the challenge.