If the engine has not come to grief in the past and now the fan no longer cuts in as often, then the engine is working less efficiently.
Sorry but I don't agree. The fan should only come on when the temperature has gone over the optimum temperature and then bring it back down into the correct temperature range.
In normal conditions when the car is moving at anything more than a crawl then the fan shouldn't be needed if the cooling system is adequate and working properly.
I should probably have prefaced this post with IMHO.
