What is the point of spraying Line-X on the underside?

Stopped by my local Line-X shop, they were trying to get me to spend $200 to spray the underside. Not that that's a huge sum of money, but I'm curious whether this is worth it and what exactly the spraying of the underside do.

I do live in a climate that snows in the wintertime... does this spraying of the underside actually help?

Anyone gotten this done before?

 

Not sure it will do much for to protect better. spend the extra money too do in front and back dog leg area and along and below your sills to prevent winter stone chips. On toyota’s The already have heavy film on the lower body.

 

Does it not help prevent rust or keep the salt off?

 

Fluid film is what a lot of other guys have used