This policy setting allows you to send keepalive packets associated with the Mobile VPN while roaming. The Mobile VPN application ...

"This policy setting allows you to send keepalive packets associated with the Mobile VPN while roaming. The Mobile VPN application automatically sends keepalive packets to keep the connection always-on.  Sending keepalive packets allows push applications such as remote device immediate wipe to work. If keepalive packets are not sent, applications that require push functionality will not work.  Note: Sending keepalive packets while roaming may incur additional data-transmission costs, depending on the service plan.  If you enable this setting, the device will send Mobile VPN keepalive packets while roaming.  If you disable this setting, the device will not send Mobile VPN keepalive packets while roaming. In this case, the Mobile VPN will send traffic only on demand, as specified by applications on the Windows Mobile powered device.  Note: Disabling this setting does not block all traffic while roaming. There might be traffic flowing over the Mobile VPN connection triggered by applications on a Windows Mobile powered device, or by the user.  If you do not define this policy setting, the default behavior is to disable sending Mobile VPN keepalive packets while roaming."