According to Clark's GSM, the valve opens at 58C to start the vapor recovery system ("G" on the diagram).
Fuel and Vacuum Line Diagram (1985.5 and Newer N/A 944s) I assume early 944's are similar.
That diagram calls the venturi-like thing an "ejection pump." Item "D."
If you bypassed the valve and ran the vapor recovery system continuously, that probably wouldn't hurt anything. Maybe it would impact starting? I dunno.
Mine I just blocked off the lines so I wouldn't have a vacuum leak - which is also seems to work okay, but may affect emissions.