Hi,
To start with I am not a tax pro but here is my understanding of depreciation. First off lets take the truck example from above, that example assumes that you are depreciating to zero which you can do to increase the write off however you have the option to assign a salvage value to that truck. The salvage value is the amount that you think the equipment will be valued at the time you sell it. I.E.
Buy a truck for $30,000 if you depriciate it to a salvage value of $0 over seven years you are taking a deduction of $4,285/year, if you keep that truck for 5 years and then sell it in the current market with strong used car values you might sell it for $20,000 however you have claimed a depriciation expense of $21,425 for a true salvage value of $8,575. The Gov. sees the differance between your claimed value of $8,575 and the value that you actually sold the truck for of $20,000 and will not allow you to deduct the $11,425 differance from your taxes and they "Recapture" that in the form of taxable income. If you want to avoid that tax recapture at the time of sale then when figuring you taxes you simply adjust the salvage value to something reasnable, you might figure that if you keep a truck for 7 years it will be worth half of what you paid for it and assign a salvage value of $15,000 to that truck then your math looks like this.
30,000 - 15,000 = 15,000 Depriciation expence,
15,000 / 7 years = 2,142/ year
Now if you sell the truck in 5 years here is what it looks like. Sale value $20,000 total depriciated $10,710 ($2,142x5) leaving a salvage value of $19,290. This gives you a recapture of $710 which is not much to be worried about.
It all depends on your tax stragity and how long you are going to hold an item. This is why you need a good CPA that can advise you on not only how to save money on taxes this year but also how to avoid being blindsided in later years.