Lead solder melts at a lower temperature than lead free stuff, which can in turn reduce the potential for ‘burning out’ the carbon track inside of a pot when wiring it up.
The downside is that gives off poisonous fumes, and should be used in a well ventilated area. Be sure to wash your hands thoroughly afterwards too.
My own ‘top tip’ for soldering pots is to ensure that they are fully counter-clockwise before you start; this limits the amount of heat that can be transferred to the track inside them, this protecting them.
If you’re using lead free solder then your iron doesn’t need to be much hotter than about 220 degrees, lead solder will be fine at about 180/190.