Here's a quick handy tip.
I use labels extensively in FCP. Red generally meaning bad and green generally meaning good with other colors to indicate variances thereof. However, if you create a new multiclip and then highlight that multiclip in the Browser, then assign it a label, FCP will also likewise label the clips that comprise that multiclip and are also set as Video and Audio source in the viewer (even it they aren't loaded into the Viewer).
I'm not sure how handy this is, but since you can highlight a multiclip in the Browser, give it a label, and FCP will also label the clips choosen for Video and Audio so you can see which are being used -I guess- at a glance without having to open that multiclip and load it into the Viewer. Maybe not practically handy, but fun to know I suppose.
It seems a tad buggy at times, where you have to load the multiclip into the viewer to get some kind of labeling voodoo to reset if it only labels the multiclip itself but overall it works.