Clutch cycling switch

This isn't an a body but I typically get better results here, there aren't any D150 sites that compare to what this site is to an A body....

I'm adding factory AC yan 85 D150.
I have most all the parts off of multiple donors of 80s factory ac equipped trucks. Just missing a few things, have multiples of other related parts.
One thing I don't have, and have seen on some vehicles but not others ... A "clutch cycling switch"
Different than the low pressure cutout switch. I know I need that.
This is a square block, with 2 terminals, and has a capillary tube that slides in along side one of the lines near where it bolts to the expansion valve. It's wired in line with the "hot" lead to the clutch.
How important is this, what happens/don't happen if I don't add this, and run the "hot" straight to the clutch /rather than thru one of these?