A space link is mainly used around the mid to late-term game. It's units can be used for many things such as battling, sabotaging, plant making, etc.
Defensive and Attacking Tactic(s)
Due to the space link's health, it can be easily destroyed by a nuclear missile. To give it better protection, it should be planted near a middle of a well guarded base and if possible, should be covered by a shield for extra measures.
When planning to attack a place, there should be backups of space fighters or motherships bought on the space link just in case they get damaged to a point where they are at critical or no health. By doing this, this allows an army to gain back its troops fast without having to retreat.