I've been thinking about this a lot and finally managed to work it out (I think). I was running into lots of check raises on the with people slow playing monsters. Net effect has been to transfer red line winnings (they fold to river bet) to show down winnings.
Looking at the graph though, my win rate seems to have slowed by doing this as I'm not getting any river value from

: Ax missed draws who think that A high may still be good
: bottom pair hands when my draws miss. Checking behind just gives them a showdown win instead of having to make a decision as to whether their second/bottom pair is good or even high cards as they missed their draw too.
: From my top pair hands where I protecting myself against two pair and sets.

the advantages are people slow playing monsters don't get to check raise me and put me to a decisionto fold or call that extra river bet. There do seem to be an awful lot of people slow playing their monsters lately and checking behind on the river has shown me this but for every time I think I did the right thing checking behind there I end up thinking that I'd probably have won the hand if i'd bet the river as they'd have folded the air /bottom pair type hands.

This is something I'm going to have to work on to try and figure out who to check behind and who to bluff on the river having shown aggression throughout the hand.