If you sleep or hibernate your system - use this instead! (You paid for it + it's better!) If you never use sleep and always shut down, you can remove it :) Plus it'll last anywhere up to 15+ days, depending on your battery capacity and its charge. Instant on saves your Windows session and your work (like hibernate), but still boots the system in 2-3 seconds (like sleep).
Hibernate saves your Windows session and your work, even if your battery dies, but it takes just as long to boot as a cold boot.
Sleep boots the system in 2-3 seconds, but doesn't backup your work, so in 2-3 days if your battery dies in sleep mode you lose unsaved data. Do you have the Windows gadget running? It'll tell you the anticipated life with it on compared to standard Sleep.
