I like to have an idea of what costs are to help me decide when to buy my next truck. If I've owned a truck for 2 years and it works out that selling it now the depreciation is going to be $16k over 40k miles I might be motivated to keep it a little longer. If I have an opportunity to sell such that the depreciation is only 10k and the new model truck is significantly improved over my current truck I might be willing to sell it and buy a new one even though keeping the old one longer would likely be financially wiser.