The most important reason to wash, rinse and sanitize a meat slicer or knife is to:

The most important reason is that it will reduce the pathogens on the meat slicer or knife which have settled there and it will reduce the risk of getting a viral infection or any other kind of sickness.

For sanitizing one can use simple hot water with at least temperature of 171 F and dip the item into that water for at least half a minute. There are other methods as well to clean the items.