Can I attatch my garden hose to a hose bib on the water main?
Of course trying to determine why something was done years ago is speculative. My guess would be that the valve on the left was the original shutoff. The hose connection may have been a whole house drain. This would allow you to drain the plumbing in the event of a no heat situation or long term absence. The two yellow ball valve were likely added during a meter upgrade or when it was determined that the original shutoff did not completely stop the flow of water. My primary concern with using it would not be pressure but  the age of the valve.It looks older than the valve on the left based on handle design. It is possible that it may leak when you try to shut it off.