By lobbing missiles on Tel Aviv he was hoping to break up the US-lead coalition by bringing Israel into the fight. Saudi Arabia would have had a difficult time allowing us to use their bases if we were fighting on the same side a Israel. Syria probably would have turned on us. It might even have gotten Iran to help him.
In Kuwait he was practicing a scorched earth policy in the hopes that it would slow us down and make our military maneuvers there more difficult. If you study military history, you will see that it is a has been a commonly tactic since ancient times.