If 2 teams play at the same venue then when you create a schedule you don't want them both playing at home at the same time. For example, if you have 2 teams "Valley A" and "Valley B" that both play from the venue "Valley" when you develop your schedule whenever A plays at home then you want B to be away (road) and vice versa.
If you are using the Template Scheduler then this is managed via a pairing system. It doesn't use the venues of the teams. Create your team pairs in the "Venue Sharing" step. This could be teams in the same division or in different divisions.
If you are using the Advanced Scheduler then make sure both teams share the same venue and not a duplicate venue, the advanced scheduler will never double book a venue. To check the venue / teams setup: click on 'Manage' on ADMIN HOME next to the division. Edit the team to change its venues.