Does load balancing affect incoming sessions as well?

Hey all,

Looking to supplement our existing office WAN connection with a cheaper link to handle non-essential services like employee web browsing and streaming. Is the XG's load balancing smart enough to not mess with incoming sessions? So, for instance, if a connection comes in on our essential services link for an internal web server, will I have to create a policy to make sure return packets aren't routed through the supplemental connection? Are there any other gotchas like this I'm missing? Our VOIP, some internally-hosted business software, and SMTP traffic is all configured for the essential link and I plan on leaving it that way - just want the supplemental link to handle outgoing sessions when somebody decides to download something huge or leave youtube on forever. If you have done this and have any feedback, I would love to hear that as well.

Thanks.