The first big con of Wayfair is the pitiful salaries they offer most entry level hires. Most entry level jobs at Wayfair pay several thousand dollars less per year than comparable roles at other companies. As a result, you often see people leaving on a regular basis. For example, in my department (of around 50 people) I've seen five people leave voluntarily and get replaced by new hires within the past couple of months I've been here. Some people leave very quietly, and you often don't realize it until you see a new face in the pod.
The benefits, while okay, are not great. The 401K match is pretty generous compared to other companies. The employee health insurance plan is pretty pitiful, and heavy on co-pays.
Internal tools break down on a regular basis, inhibiting work from getting done and forcing managers to postpone projects so that teams can just get through their day to day work. The system is over ten years old, written using the old ASP (which Microsoft doesn't even support anymore). They are trying to rewrite everything in PHP, but that has been a slow and arduous process. Instead of developing new software to support new processes, engineers spend most of their time fixing creaky old code so that everyone can just get through their day to day work without having the tools die on them.
Furthermore, given that most of the company's software development is relegated to maintaining old code, most departments have to grapple with a lot of manual data entry when new processes are introduced without the software backend to support them.
Communication between different departments of the company is also another major problem, to the point where most departments don't know what other departments are responsible for. This can create friction, and given that the company is constantly awash with new hires that aren't well drilled enough on what their roles and responsibilities are, this creates a constant web of confusion and never-ending chains of emails.
While there are many opportunities for people to move laterally across the company, mid-level opportunities are pretty rare, and most people don't get past "senior associate" in terms of rank.