Research fellowship after undergrad helps with PhD admissions? Does taking a year off, to work as a junior research fellow or as a research intern, immediately after one's undergrad help with admission to a better MS (research track, not professional) /PhD program?
If it helps, the field in question is computer science, specifically at the intersection of computer vision and machine learning.
I don't see how it could hurt. The degree of added value most likely depends on what your background is prior to the year as a researcher. If you already have a very strong research background as an undergraduate, an extra year of experience will not help as much as if you have very limited research experience. 

I suppose it also depends what you get done during that year. It certainly helped a former student of mine, who didn't get into his desired programs straight out of undergraduate. He took a year to work as an RA in my lab, wrote a first-author PNAS paper, and then was admitted into the top program in his field.