Why it matters on your quote
When a system is replaced, the old line set is either replaced or reused. Reusing it can be fine if it is the right size for the new equipment, in good condition, and properly cleaned, pressure-tested and evacuated. Old lines can hold contaminants or be the wrong size for newer refrigerants and equipment.
Line sets are often left off quotes or added later as an extra, so it is worth asking how they will be handled before you sign.