Apps that you have in the background often times don’t continue to run and resume when you switch back.
Location services can be fine-tuned to only be used when you’re using the app, see settings-privacy.
There is no task manager, it’s called the app switcher. Its intended purpose is in the name. While you can of course micromanage apps and force them to close there is hardly any measurable difference in device performance. I only force quit apps if they somehow have a problem and otherwise I let the operating system do its job.