Right now we have about a 25-30 PC network, connected to the internet with a run-of-the-mill SonicWall Firewall/Router device. There isn't much filtering / blocking other than outgoing SMTP (for viruses etc.). I recall reading that at some point a network/company reaches critical mass and needs to send things through a web proxy/gateway... but not why!
My guess is maybe for content filtering (don't visit porn sites, etc.) and/or virus stuff (so they don't download virus infected files), but do we need a dedicated device for that? Why won't things like Cisco ASAs do the job? What other reasons would we have for doing that? How might I determine if/when we need to move to a web proxy?
Currently we have no plans of monitoring/limiting web access and each desktop has antivirus installed.