Depreciation reduces the value of assets on a residual basis. It also reduces the profits of the current year.
Depreciation indicates reduction in value of any fixed assets. Reduction in value of assets depends on the life of assets. Life of assets depends upon the usage of assets.
There are many deciding factors that ascertain the life of assets. For example, in case of a building, the deciding factor is time. In case of leased assets, the deciding factor is the lease period. For plant and machinery, the deciding factor should be production as well as time. There can be many factors, but the life of assets should be ascertained on some reasonable basis.