Pros
The company offers a variety of projects that may fit your individual skill set where you can be a subject matter expert. Being a SME can increase your billable time and you can become a go to consultant.
Cons
The firm submits Requests for Proposals and Requests for Quotes like any other and unless there is a strong project pipeline, you can find yourself "on the bench" and waiting for a project to come through that fits your skill set. The model of many of these consultancies has changed whereby they maintain a limited amount of full time employees. If you can't afford unpaid down time and require a consistent paycheck, identify the pay structure and questing the project pipeline up front. Who wants one limited period project and then have to wait for another project matching your skills to roll in after a 2 month wait?