Todd Atlas of Sound Pure walks through blending two mic pairs on a grand piano: an ORTF cardioid pair placed close over the strings, and an omni pair pushed back into the room.
The cardioids grab intimate, detailed string sound, while the omnis capture the room's natural diffuse character. Played separately, you hear exactly what each pair contributes on its own.
The real value of this setting comes in the blend. Starting with the close cardioids and gradually bringing up the room omnis shows how the two signals combine to create depth, adding spatial dimension without losing the detail up front.
This close-and-room miking approach is a transferable idea beyond piano: layering an intimate direct source with an ambient room capture gives you control over how natural and spacious a recording feels, decided at the mix rather than locked in at the mic.