I've done delayed cord clamping several times. In general I believe it's a good thing. Helps reduce the risk of anaemia as the extra blood is transferred to the baby, helps prevent sepsis in newborns and it gives them extra iron so can help prevent iron deficiency for the first 6 months or so of their life.
However, there is a downside (as I discovered to my youngest childs cost) especially if your baby is premature and you have gestation diabetes as it can increase bilirubin levels and cause jaundice meaning an increase in needing phototherapy shortly after birth...
Most of my babies who had DCC were absolutely perfect (although a little red from the extra blood in their system), however, my youngest who was born at 36 weeks was very ill for a long time. I had uncontrolled Gestational Diabetes though that was not stable despite insulin and between that and her prematurity it resulted in her having very severe early onset jaundice which required high intensity phototherapy. Then several days after being discharged she had to go back in for more high intensity phototherapy (ended up under high intensity light AND a bili bed and on the verge of needing a transfusion).... She was extremely red for the first month or so of her life too and it was generally believed between all the Drs who's care we were under that a lot of her problems were as a result of delayed cord clamping.
That said, would I do it again next time? Yes I would! For me, the benefits in the extra Iron far outweighed the small possibility of jaundice.