VO2 max tests are pretty cool - if you enjoy high intensity exercise. You don't need to have one done to evaluate performance, but it does act as a good reference tool for training guidelines.
Here's the blurb I wrote in the description:
VO2 max absolute units : 5.45 L/min
Workload at Failure: 14% grade, 8 mph (last stage of Modified Bruce Test)
Max Heart rate: 194 bpm
Blood Lactate at Failure: ~ 19.5 mmol/L
Bodyweight: 190 lbs
VO2 max relative units: 63 ml/min/kg
A VO2 max test attempts to measure your maximal oxygen consumption i.e. aerobic capacity of your cardiovascular system. Fitness, genetics, gender, age, and body composition all play roles in a person's value. While VO2 max is great for creating a sort of reference for training, it is not a great indicator of aerobic performance. A person can yield a high VO2 max score, but not be able to sustain a high % of VO2 max for a given time.
If you want to evaluate cardiovascular performance & endurance, one way would be to see how long you could last at 80% of the VO2max workload. This weens out some factors such as bodyweight and efficiency - both of which affect performance but not cardiovascular conditioning.
VO2 max in relative units scales significantly by variance in bodyweight. A subject's bodyweight could vary up to 40 lbs while having the same cardiovascular conditioning and absolute VO2 max in (L/min), but would have drastically different relative VO2 score.
Let me comment a little more, and add a better link to hiking.
You don't need to be training for a VO2 max. You should be training in a way that optimizes around the hike / climb / run intensity and duration that you are focusing on. 30 second sprints might elicit improvement in VO2 max, but they are hardly going to do much for multihour endurance activities. 5-6 minute interval runs, however, can improve both endurance and VO2 max. The point is, proper training will lead to improved endurance and increased VO2 max as a byproduct.
For elite athletes looking for every edge, I'm sure very specific training protocols could call for specific VO2 max training. But for most of us mortals, don't worry about it. It helps to know what your max output is so you can set training paces for intervals (i.e., run at 90% VO2 max for 6 minutes, rest for 3, repeat), but you can do that with heart rate alone.
Even for hiking, intervals of 5 -10+ minutes can yield great results. This relates to the post below talking about anaerobic and aerobic energy pathways. A 5 min interval will be at an intensity high enough to use up your anaerobic capacity in the first 2-3 minutes, then leaving you with 3-4 minutes of high intensity aerobic training. The key is to get to aerobic (high heart rate) stages for at least a few minutes to get a sufficient stimulus to improving aerobic endurance. Intervals of 2 or less minutes may not get the same aerobic workout.
A few intervals in a quick 1/2 hour hike up can vastly improve your endurance on long treks on the weekends to come.