With your nice R44 raven II, you have fuel injection and no carb icing to worry about (unless you are very unlucky and get inlet icing!)
I am lightweight, 135lbs and find that solo I am often pulling only about 19" MAP. I tend to keep the carb heat on most of the time unless I know I am going to be cruising fast.
I am also paranoid and am trying to keep ingrained a habit of reaching down to pull up more heat every time I am making speed or power changes downwards, or look at the gauge and see it at sub 20".
I did read once that excessive use of carb heat can cause detonation, but I'm not sure that it is a problem in UK temperatures.
BW