You have an option to deduct
your actual travel expenses - that include all receipts, insurance, depreciation etc, or
use mileage rate.
You may select either method that provides you with better deductions.
Most people use mileage rate deduction because of simplicity.
Please see more details in the IRS publication - 463 - http://www.irs.gov/pub/irs-pdf/p463.pdf
If you want to use the standard mileage rate for a car you own, you must choose to use it in the first year the car is available for use in your business. Then in later years, you can choose to use either the standard mileage rate or actual expenses.
If you want to use the standard mileage rate for a car you lease, you must use it for the entire lease period. For leases that began on or before December 31, 1997, the standard mileage rate must be used for the entire portion of the lease period (including renewals) that is after 1997.
You must make the choice to use the standard mileage rate by the due date (including extensions) of your return. You cannot revoke the choice. However, in later years, you can switch from the standard mileage rate to the actual expenses method. If you change to the actual expenses method in a later year, but before your car is fully depreciated, you have to estimate the remaining useful life of the car and use straight line depreciation.
Generally - you may depreciate the property that is used for business - I agree,
however - if the property is just stay ""in case" and you do not use it - if the IRS would audit you- your deductions may be disallowed.
You may depreciate the property that you use in business - not the property that you actually do not use and use very little.
That doesn't mean - you can't deduct depreciation - you can - but you should be well prepared to justify the business use.