It's important to save your fleets when you're not OnLine. Reason as long as your fleet is still on your home planet, your fleet is included into a potential battle against an attacker! Additionally your fleet is visible on a spying probe and the attacker knows exactly what he has to count on. If your fleet isn't saved, the fleet will be included in any attack taken place at your planet. This could potentially lead to your fleet being fully destroyed. How to SAVE your Fleet? Have fun!