Question

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

Answer 1

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.

Answer 2

The most important reason to wash, rinse and sanitize a meat slicer or knife is to: prevent it from harboring and breeding harmful microorganisms such as bacteria.

Washing or sanitizing a meat slicer or knife after use is very important.  When a meat slicer or knife is not cleaned or sanitized regularly, meat can accumulate in it and allow harmful microorganisms such as bacteria to grow. The organism (bacteria) can contaminate foods and lead to foodborne diseases.