It's totally your choice. It depends on what you want to accomplish in the game, how strong you are in relation to your enemies, how high your BB is, etc.
I only release satellites if they're of no use to me, and/or I'm trying to reduce BB, and/or I feel the territory is too difficult/expensive to defend.
Here are some things to consider.
Does Russia have cores on any of the provinces you just annexed? If not, they're less likely to attack you in revenge. So if you're worried about Russia attacking you, maybe you could release part of the territory (if part of it forms a releasable country) but keep the rest of it.
Can those satellites defend themselves against their most likely enemy? It's unlikely the Baltic states or Poland could defend against Russia. If attacked, they would ask you for help and you'd be doing most of the fighting. They would most likely be conquered, leaving you no better off than you were before. So using them as a buffer zone might not work out.
Is the territory profitable and useful? If there are POPs working and making money for you, and if there are soldier POPs you can use, then you should probably keep the land.
If your BB is too high to profitably trade tech or land with other countries, releasing satellites could help. If you're trying to trade, you don't want BB much above 20. If your BB is really high, like over 100, I don't know if it would be a good idea to release so many satellites to get it back down. Your country would probably shrink too much.
One good thing about having a satellite buffer is, when you are attacked, if you don't call for help from your satellites, you can hide in their territory. So if you release the Baltic states and Russia attacks you, you can invade Russia from that territory, and the Russians won't be able to pursue you if you need to retreat.
Personally, I wouldn't release territory contiguous to my country. You don't need a navy to defend it. If it was on the other side of the world and useless territory, then I would consider it.
