A quick web search will find lots of vacuum gauge information:
http://www.centuryperformance.com/vacuum.asp

Never had an A/F meter on a carbed engine but do have one on my 22RE. I find it rather handy for monitoring engine operation and finding optimal operating conditions. For example nice to find out if the ECU is running in open or closed loop mode in different gears up a grade.

I have had vacuum gauges on most every vehicle I have owned over the years. Good thing to check for a feeling of how hard the engine is working and if you have any extra power in reserve, like when pulling out to pass someone. If the gauge is down under 5" Hg, not much is going to happen when you mash the gas pedal down. The vacuum readings (and engine power) will vary with elevation and the gauge can help you see that power drop-off and you can adjust your driving accordingly.