Large consulting firms
Hiring a large consulting firm to do a software project may give you a warm feeling of safety: "They've been around for a while so they must know what they're doing, and they won't go away in the first place. And if things get tight close to the deadline, they have additional resources that can help".
Sounds great, but there are some issues to consider.
One is that you don't always get the person most suited for your project's specific needs. What you do get is their first guy that happens to be available and whose competence is not totally disjoint from your specific needs.
What you also may get is a number of people whose added value is hard to evaluate. "To be effective, we would like to follow our Digital Conversion Process. Next week we'll bring our top Strategic User Augmentation Designer and one or two Mobile Data Conversion Analysts for a couple of sessions where we will prepare everything for the prerequirements phase."
Another thing to look out for is virus consulting. This can happen when suddenly the need for a specific skill arises in the project, and the LCF just happens to have such a person eagerly waiting to jump in and help you out. Don't be surprised if the project manager gets a commission for each colleague he manages to squeeze into the project.