No, the resource they use (RAM) would be wasted if it didn't hold anything at all. RAM doesn't consume any more power due to an app being loaded into it.These tasks are started and sit in memory so they'll open faster when you decide to use them. In the meantime, the resources they're using are wasted.
If you're rooted and do a "ps", you'll see that just about everything which is loaded is also sleeping, doing nothing. An app which wants to do occasional updates (i.e. check email), will ask the OS to wake it up periodically. This is done through ScheduledExecutorService. While it's sleeping, it is not wasting resources.
It takes more resources for an app killer to occasionally sweep through processes and kill them than to just leave the process alone, sleeping.
Yes, there certainly exist apps which are incorrectly or poorly written, and which you might want to kill. If you find one, uninstall it and don't look back.
I've never had any issue with Maps running the GPS when it's in the background. I changed my browser home page to be empty, so no Google page polling for location (you can also close windows if you want to be sure).