Rheumatoid factor in rheumatoid arthritis is important because -
"The chief value of the rheumatoid factor tests is in the assessment of prognosis : persistently high titers herold more serious disease including extra-articular features". — Apley
RA factor is associated with bad prognosis
Absent RA fact6r rules out the diagnosis of Rheumatoid arthritis
It is very common in childhood Rheumatoid arthritis
It correlates with disease activity