We put all our clippings on the compost heap. If you now your lawn once a week there isn't as much clippings as what there would be if you left it grow longer. I remember as a little girl that my Nan has this big garden bed full of chysanthamums and she would always spread the ash from the fire over the garden bed. I had no idea why she did it at the time, but a while ago I read that you can use it because it acts as a liming agent. So if you have acidic soil, spreading ash is very beneficial but you will need to check the PH levels of your garden soil first.