Feature request: source panel "free play" toggle, allow previewing media while scrubbing timelines

My big idea is to have the source panel have the option to "free play". Often, I'm previewing music or sfx tracks in the source window and I'd like to scrub through sequences/ edits to see if the music will fit the raw footage. Why is this not a feature? It would be a simple button on the bottom or a setting in the wrench in the source panel.  Thanks.