Additionally to the other comments, the decision to use management software relates to the cost of one's time; in other words, what opportunity cost is your time / money?
But in terms of time, experts e.g. property managers may underestimate the time it takes the amateur to (re)learn infrequent tasks. Since I list some of my (very few - I only have 3 residential units and my commercial ones are all managed by others) units every 2-3 years, I forget how to do it, and even standard operating procedures change a lot at that frequency, rendering them much less useful. For example, It may take me 10x as long to do the work of someone who does it every day. This applies to listing a unit for rent, qualifiying leads, the administrative side of showing property, screening tenants, and leasing. Well designed software for your problem would not only add tech, but process, and not only in the realm of time savings.
Good software, as one earlier poster wrote, can do it better. For example, syndicating your listings to a much broader audience, making the application faster, improving applicant experience, making maintenance requests get done more smoothly and quickly. This could result in higher quality tenants sooner and keeping them longer, all which have more than quantifiable effects.
But back to your question: I don't know. When I evaluate a software, I first build a list of the most time consuming aspects of my existing work process. Then I brainstorm options in a people/process/technology framework. Buildium at $55/month/$660/year is a relatively low cost threshold given opportunity cost of my time, so I'll likely consider that and if so, could report back..