The choice of which method a company will use to calculate depreciation comes down to the objective they are trying to achieve. A company that chooses to use the straight-line depreciation method is probably more concerned about keeping its book value higher. This method will help keep their revenue numbers higher and give their earnings per share (EPS) a lift.
On the other hand, a company may be looking to decrease its taxable income. In this case, they may choose an accelerated depreciation method that will allow them to lower their income and provide tax savings.