[LGM]

I like CSM on a Satellite at planets in Simultaneous games early on. True, the attack might come from the other side of the planet, but the attacker cannot be sure, so he has to consider the Satellites in planning his attack. Use the left over 20 KT for PDs or some other 20 KT beam type weapon so they will not be as vulnerable to Fighters later on.

Satelittes are great at Warp Points, but you have to build a ship to deploy them

If you are using Emergency builds early on (build colonizers quickly or ship yard bases), you can build Satellites during the slow turns as extra defense.

If you are on a large or huge world, W. Platforms perform better than Satellites. On smaller worlds you need the cargo space to make units(Troops, Satellites, Mines and Fighters), so Satelittes are a better static defense.

Once I have Mines or Fighters, I prefer building those for defense.