Join Combat is very hit and miss. On the rarest of occasions it'll send me to a decently populated fight. Other times it'll send me to a 96+ friendly zerg rush. Ooor it'll send me to places like this.... where we neither have population, nor can even capture the base. All because someone decided to put a Sunderer there. How is this helpful? What if a new player spawns in, presses Join Combat, and this is where they end up? What kind of impression is this going to give them? This thing needs to be reworked.
It usually puts you in a spot where many of your faction are. On off-hours small fights qualify, otherwise it just picks the biggest 5v1 zerg and puts you there.
The problem is that this was at a time where one continent was open, there were over 600 players, with 200 on each side (this wasn't taken today). You can even see from the continent population, and location population numbers, that TR were near enough the same as VS in terms of continental population. There were other fights it could have placed me in with better population. Overall, whatever its reason for doing so, it certainly needs a rework.
Instant action sends you to the hex where there are the most friendlies. If you are already in that hex, it will send you to the second largest concentration of allies.
I use this a good bit too because often times I just want to hop in a fight. I as well find it hit and miss and I think it's because it is a very simple mechanism. Works well for me during peak times but in off times or when a continent just opened up not so much. BUT, I don't think it needs changes really. While it is an easy way to skip into a fight it's not a very strategic option.
How to use Join Combat.. Step 1. Don't. Step 2. Manually redeploy to the fight you want to go to instead. Step 3. If you are unable to go to that fight you want to go to, hit the Join combat button and see if it takes you there. If so, Yay!!! If not.. Cancel and get you *** a Valk