If your 1st team has full condition (99%) and you see your team will regain 6+ before your next game, train the first team once.
I have a training schedule I find nicely balanced and fills bonus quick while taking on average -6 each time.
Also, there is a training bonus x2 which will take less turns to fill bonuses, usually top right corner I think.
Try that out, hopefully you'll find things a little better.
Yeah, purely for bonus nothing more. I like bravery so I try to train that in defenders, not sure why. Just like blocking freekicks and shots I guess lol. I train my first team once when they're full condition and it won't affect condition for matches.