Well yes, of course you should, but not for the reasons usually quoted by environmentalists.

Cutting out short trips to the shop and school does not substantially reduce your car’s emissions as much as, say cutting out long trips or car commuting. Although there is an impact on your catalytic converter. However, there are health benefits of walking or cycling to the shops (or to school if you have kids). If you walk just an additional 150m per day, you will burn sufficient extra energy to equate to 1lb weight loss per annum. This will also help alleviate the “school run” traffic congestion (ah, for the summer holidays!).