If you shoot a compound bow much, you know how quickly a poorly maintained bow string dries out and frays.
Now imagine if your compound string slid across a hard surface every time you shot. You'd have to replace your string about once a week if that was the case.
Well, that's exactly what happens when you shoot a crossbow.
Crossbows are fairly maintenance-free, but the string is extremely susceptible to wear. While the contact point with the rail is generally served with a tough material, it will still wear and dry out if not taken care of.
Pretty much all crossbows come with a tube of rail lube, but very few shooters actually use it.
It takes about 20 seconds to put a dab of rail lube on your finger and smooth it along your crossbow rail. That little chore will more than double the life of your crossbow string.
Like a compound, your crossbow also will benefit from regular waxing of the cables and strings, too.
Also note that rail lube and string wax are not the same. Rail lube is designed more to reduce friction, while string wax and string-care products are more for protecting the string and locking in moisture.