Film is a visual medium, right? It's purpose it to be watched. Yet it begins in written form - a screenplay - to be read - so there are two very different 'audiences' during the filmmaking process. This may explain why many aspiring screenwriters make the common mistake of including 'unfilmables' in their spec script.
'Unfilmables' refer to information or elements written into a script that cannot be visually represented or heard on screen. And if we can't see it, it probably doesn't need to be in your screenplay. Trust me, no script reader wants additional unnecessary words to trawl through, so let's take a look at some common examples and how they can be improved.
While the majority of these examples are big no-no's, yes, you can absolutely use 'unfilmables' to add flavour to your writing. A couple of smilies, metaphors, and a bit of essential background knowledge (especially during character introductions) here and there can definitely add to the enjoyment of the read, so I'm not saying don't ever include them - just use them sparingly!
Always keep in mind that the audience are watching the show/film, they're not reading the script, so 'unfilmable' info may be taking up precious space on the page that could be better used to craft vivid, engaging scenes that can be translated directly onto the screen. Do this, and it'll help keep your script lean and the script reader happy.