Most shops flush the entire system in case metal fragments entered the system from the failing compressor.

I have flushed several systems due to failing compressors and in most cases there was metal slurry in the oil in the system.

Most shops do it just to cover their butt.
Better to be safe than sorry.
I would spend the extra time and money to flush the system.
We used and alcohol based solution, the name escapes me, but we filled a metal cyllinder with this stuff and flushed the systems out with this stuff hooked up to compressed air, and it dried the lines as it cleaned all the oil and metal debris out of the system.

I'm sure someone on here will know what it's called.
If you have alot of oil and metal fragments in your system, you may risk contaminating your system.