It has to be tackled at some point, so I'm thinking;
Fleets basically have a limited number of Fleet Actions they can perform per turn, which is determined by the Tech Level/Tier of their Engines. The default engines give a ship/fleet 2 FA. The maximum amount of FA acquireable will probably be 4, barring Artefacts.
Example action costs;
Cost | Action
1 FA | Move between systems inside a cluster (blue connection)
2 FA | Move between clusters (yellow connection)
1 FA | Engage enemy fleet
1 FA | Reorganize fleet (add/remove ships) (this cost is applied to both fleets if applicable)