As I see it, there are three reasons an investor owns rental property.
1. Cash Flow
2. Appreciation
3. Tax Benefits
Rental property investors buy the cash flow. You need a positive cash flow to sustain the property while you wait for appreciation. If there is a positive cash flow, then your tenants are buying the property for you, and paying all your costs of ownership and rental operation. Eventually, your tenants pay off your debt and you own the property free and clear. Can't get there without positive cash flow.
Appreciation does not happen every year, nor does it happen at a constant rate. Indeed, over the short haul, appreciation is not guaranteed. Hold the property long enough, and the property usually does appreciate. Now, appreciation does not help you if you bought during a market peak and are forced to sell at a market bottom. Most of us are not forced to sell when the market is soft. If we sell, we nearly always sell at a profit -- so, appreciation is usually a payoff for the rental property owner.
Tax Benefits come in several forms. The largest immediate benefit is the depreciation expense. Depreciation does not cost me anything, does not take any money out of my pocket, yet it does reduce my taxable rental income. Even if I have a negative income, depreciation makes that tax loss even greater so my net passive loss allowance is larger. Either way, I have a lower tax bill than I might have otherwise without the depreciation expense.
I agree that after a certain number of years, the depreciation expense goes away. But by then, I will own the property free and clear, and will have added other depreciable properties to my portfolio with the excess cash flow..
If I am in the 25% tax bracket, then when the property is fully depreciated, Uncle Sam will have "paid" me 25% of the cost of my rental dwelling structure through income tax savings, while letting me keep 100% of the title.
There are other tax benefits too. Rental property owners enjoy capital gains tax treatment when their property is sold in a taxable event. The capital gains rate is a preferred rate that is always lower than the rate charged on your ordinary income, including your taxable rental income.
Rental property investors can defer capital gains taxes indefinitely with a 1031 exchange.
None of these reasons should be the single deciding factor in deciding to become a landlord. If you have one, you usually get all three.
That said, if you are going to pick a single reason to NOT buy a rental property, it should be a negative cash flow. Even a negative cash flow property has tax benefits and may appreciate over time, but it is not generally an efficient use of your investment capital. If I don't have a positive cash flow, I don't even bother with the property regardless of the potential tax benefits or potential for future appreciation.