So switch films are useful due to their effectiveness in reducing wobble between the top and bottom
housings. They also make for a 'tighter' switch, affecting sound as well.
Here is a short video that Oblotzky made a while back that demonstrates their effect:
https://gfycat.com/unlinedsmartleafhopper (bottom row is without films, top row has films added)
They are particularly useful for Cherry MX-made switches, so Cherry MX Blacks, Browns, Clears, etc...
People often recommend them for some other switches.
However, ZealPC Tealios, NK x Kailh Creams, and most Gateron/Kailh made switches tend to already have a pretty tightly-fitting top and bottom housing fitment, so I personally would not bother applying films on these.