experiencing Chess on real board
you can always get a real board and practice- master games; setting up tt problems, etc- at home before playing "live otb"
At longer time control, it is almost the same. But for me, playing online blitz is more comfortable as you don't have to worry with pieces flying, illegal moves,pressing the clock with the hand that you used to move the pieces etc. In otb blitz, it is an automatic defeat if you allowed your king to be captured.
Having said these, playing OTB is fun.