Pros
It's experience to put on your resume and most people don't know how bad the place is and how worthless that experience was. So if you're struggling to get another job this is a resume filler.
Cons
Little to no training, coaching, and development and poor recognition of staff and seniors ability and achievement leading to very slow career growth based on merit. Partner's friends are promoted quickly and far above their ability. This company grew by acquiring many smaller firms but didn't integrate any of them into the existing form. Every newly acquired firm keeps functioning on their own except for payroll source and email addresses. Many Acquired firms retain separate computer systems and barely interact with the rest of the firm and do things their own way which is highly variable in quality. The whole company functions in a totally seat of the pants manner with no uniformity and the talent, processes, and work products are at the level of a small local firm and not a top ten. This top ten firm struggles with large clients due to lack of experience of it's employees. Most of their clients are quite small to me size businesses like you find at the type of small firms they acquired. That is all the managers and up can handle. The majority of managers and above were technically incompetent and did not have well developed, complete understanding of the tax law they specialized in. Many in my department were not accountants but humanities majors that good an enrolled agent title and were friends with a partner at one of the small acquired firms and got into BT that way. Managers made many mistakes and cut corners a lot. They was undercut competition on engagement price and then do a very superficial and often incomplete job of the tax work to keep billable hours on budget. I learned how to make the work papers look good but not how to properly do the tax work. This place was a literal waste of time to work at and many people were unhappy and turnover rate was high. Training of new people was poor to nonexistent. I was told by partners that managers would train me, then told by Managers what my assignments were and to go other staff for training if I needed it. I was warned about this place and didn't listen and how this warning stops your from making my mistake.