Scorecenter, and most all apps, won't affect your battery enough in the background to worry about killing them often. It's not like it's fetching scores all day in the background.
It's a good thing to be able to have the option to kill apps, but it's rarely beneficial.
Uh... actually, Scorecenter can't fetch scores in the background... sorry..
There are several ways to multi-task in iOS. There are only a couple worth worrying about.
GPS
Audio
VOIP
Local Notifications
Push Notifications
Task Completion
Frozen State
Let's handle each one by one.
GPS apps, you can tell these are running by the arrow in the menu bar. No arrow? It's not running in the background.
Audio apps, you can tell these are running in the background by the play button in the menu bar. No play icon? It's not running in the background.
VOIP apps, you can tell these are running in the background by the red menu bar. No red menu bar? It's not running in the background.
Task Completion. This allows apps to "finish" doing some task in the background. They can run at max length for 10 minutes. Then they're killed automatically. You really don't need to worry about these.
Push Notifications. Same as in previous versions. Internet based notifications.
Local Notifications. Same as push notifications, except they come from an internal calendar/alarm system. They don't use much battery and thus shouldn't be worried about.
The final one is frozen state. This is what most apps do. When you close the app it is "frozen" in the state it was just in. It isn't running in the background, it is frozen. When you reload the app it takes you right where you left off. When it is frozen it isn't using any processor power thus isn't an issue for battery life.
Point is, you don't need to kill tasks. If you see the icons for multi-tasking in the menu bar, by all means kill the task if you're not using it. But otherwise the "multi-tasking" bar is more of a "task menu" that let's you quickly switch applications without finding them on your home screens.