In the US, CVs are used largely by academics and researchers in lieu of resumes. In addition to the standard resume stuff (but usually omitting things like "objectives" and "skills"), CVs include your publications, presentations, professional service, products and patents etc., and in some cases grants and teaching experience. All of it. Unlike resumes, CVs can go on as long as needed.
I understand that the length is standard for a CV, but I can't imagine a situation where the third page of any document would change someone's mind about you in consideration for a job, grant, or other opportunity. Wouldn't it still make more sense to distribute a single page with a curated subset of your work, perhaps with a URL to a more exhaustive CV?
A CV is like a Viking chest-pounding saga about your Great Deeds. The currency of research and academia is publications, presentations, and service. You want to show that you have this in spades. Essentially, a CV is a portfolio, not a resume.
In the US, CVs are used largely by academics and researchers in lieu of resumes. In addition to the standard resume stuff (but usually omitting things like "objectives" and "skills"), CVs include your publications, presentations, professional service, products and patents etc., and in some cases grants and teaching experience. All of it. Unlike resumes, CVs can go on as long as needed.