I have 2 rental properties. Benefits of paying off early?

[Steve S.]

What are the pros and cons?

I have bought them within the last year.  I could probably pay off both in 3 years or so and would gross about $3,000 per month in rent at that point.

Are there reason NOT to do this?  $3,000 more per month of consistent cash flow would = early retirement.  

Are there reasons TO do this?