When buying assets, such as vehicles, the price of the asset may depreciate over time. Although it's not strictly necessary to put this into Microsoft money, you may want to avoid sharp dips in your 'net worth' by recording the asset and then writing off the value over time.
In FAQ Article 474, I mention the use of appreciation/dereciation and how to record it in the program. In the following article, it can be used as a mechanism of writing off the value of an asset bought for cash.
Of course, in a non-business scenario, choosing a period to write off an asset is very subjective. When I do it, I typically do it by writing off a nominal amount each month, and then reducing this nominal amount each year. It the asset ever hits a zero value, then I stop depreciating it.
With house price appreciation, then I typically use a fixed amount each quarter. However I review the asset value each year to make sure I haven't got it totally wrong. Recently having my house on the market has enabled me to put in a very accurate valuation (accurate to the point I knew how much someone was willing to pay for it).