Calculating cashflow - yearly instead of monthly

[AJ Brown]

BPers, 

I'm trying to calculate my net cash flow and it occurred to me that in the normal formulas we tend to use, we never factor in the tax write offs. If management fees, property tax, interest, depreciation, etc can all be written off (basically given back to us), then why should it be factored into the net cash flow. 
Am I making sense or am I looking at it completely wrong. 

Thanks!