mcintosh mc275 mk6 tube rolling ?

This is important with dual triodes like 12ax7 and 6922.

If both triodes are used in parallel, the tubes can be matched using both triodes together.

It's really only a problem if each triode is used separately as in a phase splitter like a long tail pair. 2nd harmonic will increase if the gain is off, but some might prefer that as 'warmth'

A real benefit is testing tubes every few hundred hours to ensure match is still close and no tube is not heading south. Additional benefit is 'cleaning' the pins and sockets from the removal / insertion.

If you want to roll tubes, you should have a tester to make sure you are comparing good tubes. 

To see what's involved in making a proper tester see ieLogical Build Images

There are simpler that do less and more complex that are mostly beyond what a hobbyist listener requires.

The uTracer, a miniature Tube Curve Tracer / Tester. (dos4ever.com)

A low cost, easy to build diy valve/tube tester | Valve Heaven

A very simple emission tester for power valves | Valve Heaven