Some communities hold gender-specific events (e.g., "men's golf outing" or "ladies' night out") and like to be able to send communications about those events to just the residents who would be interested.
If you believe your community will send gender-specific communications, you may want to ask for people's gender when they register. Otherwise, you can hide this question entirely.
It's important to note that if you do ask for gender, it will never be shown to others (including website administrators). It will only be used behind-the-scenes by our system for sending gender-specific communications.