One irrefutable fact about refrigeration systems is that sooner or later, they all need at least one access port. Testing, evacuating, charging - they all require access to the refrigerant circuit. That is where the lowly Schrader valve comes in. If you are changing out the compressor (or any other component) in a small refrigerator, you are going to want to solder a couple of these fellows in place (one on the high pressure side, one on the low).
Note: Use the valve cap (supplied) to remove and replace the valve core during soldering.