Old Art
From MechWarrior: Living Legends Wiki
Introduction
Old art, or, assets that exist in the game already. To make a new and exciting map, the experienced mapper will always resort to existing art before trying to solve problems with adding new assets.
Moreover, experienced mappers are already familiar with the quite extensive library of assets in the sandbox2 editor and didn't even had the chance to try all out, let alone dry the ideas of whats possible and at hand.