If England opens anti-french (for eg to EC) then, if germany is willing to cooperate, he bounces russia, to show he will help england against france, and not let russia to bother them.
But there are cases when germany needs a strong russia, for example turkey gets to BS, england opens to Edinborough posing no threat to Germany, it could be a good idea to make them fight.
If Russia opens north (mosc->stp) you might also support him, so he will secure scandinavia resulting a weak england, so germany can fight france.
If Russia opens weak south, you also might want to help him, because he will build south then, to support his units, slowing down turkey/austria.
As Split stated, you have to take all 7 countries' moves into count and make the decision according to that. Basically, if you need a strong russia, oyu let him in, if you have a good alliance by the very first move, you bounce.