Pros
As long as you are billable and meeting project deadlines/responsibilities, you are set and will have a lot of flexibility (i.e. working from home) and on your own schedule. Over the years, I have done a variety of office and field projects, and feel this has given me greater perspective on the environmental industry. Tetra Tech does perform a lot of different types of work.
Cons
When work slows down, a lot of onus is placed on the employee to find their own work and maintain utilization. Heavy emphasis on utilization. The down-side of this is that in any given year, your most important goal will likely be to remain highly billable and/or bring in work. You will likely get stuck doing mundane work to meet utilization requirements. Training/mentorship and employee development is not a priority. Doing good or even excellent work on assignments is not enough to significantly advance your career.