If you happen to incur an accident you will have to file an insurance claim with your insurance company which may cause your premiums to rise and thus wipe out any savings realized by not purchasing coverage at the rental counter.
Rates are typically cheaper on weekends. At one company we surveyed, you could rent a subcompact on a weekday for $64.99. When we opted for a weekend rental, the figure plummeted to a far more reasonable $22.99. If you've got some flexibility with your rental arrangements, opt for weekend rental. Your pocketbook will be eternally grateful