I'm seeing a lot of good responses. I saw one person mention it, but I wanted to elaborate on this a little. Time is my biggest expense.
For me, at this point in my career, my time is best spent finding and analyzing deals. I can make more money looking for deals and closing them, than I can doing paperwork and paying bills. It's a tough calculation to really pinpoint, but it's an important one to figure out. How much is your hour worth?
Let's say last year you made $72,800.00 and you work 40 hours a week. You'd be making $35 per hour. During your 40 hours per week, you're working on everything. You answered tenant calls, fixed things at your properties, opened your mail and paid bills, prospected for new properties, analyzed new potential deals, etc. etc. If you take a look at where you're spending most of your time and see that 50% of it is doing administrative work, and remaining 50% of the time you're actually doing work that produces the $72,800 per year, you might be costing yourself a lot of money in opportunity. In this scenario you're paying yourself $35.00 per hour as an administrative person. Could you hire an admin for $15.00 per hour to take the majority of the administrative paperwork side of your business off your shoulders? That would mean that you've got an additional 15 hours per week to go out and work on the things that are actually producing income. Not the administrative stuff that consumes lots of time! You're probably going to increase the income you bring in, significantly, by hiring someone!
