Subject: Reserves.

What will be the disadvantages of not playing my reserves in friendlies while training stamina? Will I lose general training or something?

yes, exactly that

Damn. Getting sick of my reserves atm, all need pace to be any good.

I believe they are more likely to lose form as well...

Damned reserves :(

Go for pace training than stamina. I train stamina only during season breaks.

All my team need it badly.