I am a member of a level 7 gym. There are 2 Lapras, 2 Snorlax, 1 Arcanine, 1 Vaporeon, and 1 Pidgey. The current prestige of the gym is 25,432 / 30,000. The Arcanine joined and left the prestige at about 20,500. I trained (even though I'm already a member) to push the prestige to 25,432 so far. This sets a higher bar for someone who tries to conquer this gym, right? I'm not quite sure how it works.
Does this make sense? If I continue training and can push prestige above 30,000, then I've opened an extra defender slot, but I can't control who fills it. Someone walking down the street could notice this extra slot and join. I'd hope for a Dragonite, but I'll take any extra person to help defend.
So, does training a gym that I'm a member of help defend it?
25,000to34,000, and a Vaporeon jumped in. His CP is higher than mine, so I've not really improved my strategic position. The rewards are better for being a member of a high level gym, but I'm still 2nd from the chopping block. For me, it's more "I want to stay a member of the team", not "I want my team to hold the gym". – Just Someone Aug 22 '16 at 19:31