The Wireless roaming option determines the following:
Order of selection: determines the priority of configured/known WLANs. When attempting to connect (by means of manual or automatic (re)connect) to a WLAN the device connects to the WLAN with the highest priority first. The list uses a descending order (first WLAN has highest priority).
Stay connected: enables continues scan for wireless networks. This option is required to for automatic roaming whereby the device tries to reconnect when losing the network connection.
Active scan interval: determines how often a rescan should happen.