Like 90% of all apartments in the area, we charge a pet fee: $200 when you move in and then $20 per month. There's not really a good reason to it. I know you could say that cats often do more damage to carpet, but at the same time we don't charge someone for other factors that make them more likely to damage the apartments (kids that color on walls, clumsiness, smoking). But here's the thing. That $20/month you're paying? It doesn't technically go toward your security deposit. You're just paying an extra $20 a month for nothing.
The weird thing though, is I have had two people now that have called me and refused to rent from anywhere that would charge a pet fee on principle. It doesn't matter if our rent special puts our prices at $50 less than a competing community. They would rather pay $850 a month and no pet fee than $820 a month pet fee included. It doesn't matter that maybe we include utilities. They would rather pay for all their utilities than have utilities covered and a small pet fee charged.