You do whatever the little booklet that comes with the engine says to do. That is, unless you have a really old engine. Engines nowadays have modern alloys in the piston and sleeve and have really close tolerances. They usually do not require the breakin we had to do in the old days when pistons had iron in them and sleeves often weren't exactly what you'd call round.

CNC production does wonders for the roundness and tolerances. And the piston/sleeve metals are close to magic. And today's engines come with excellent breakin methods clearly spelled out.