life of asset / life of asset is an accountant’s way of apportioning cost. ideally in the early years of life of an asset - you would have no charge for maintenance. most often, you would find maintenance costs becoming larger the older the machine gets.
the depreciation (straight-line or whatever) you read about is just an “apportioning” of the cost (and shows up on the balance sheet) since it provides you a tax break (again accounting).
for a company in the maintenance portion of its life - they would ideally like to report a bigger # as the depreciation expense (accounting), get a tax break, etc. etc. but what they actually expense out (actually spend) - would just be what they expect to pay to keep the machinery in running condition.