A compressor that can only be fully on or fully off behaves nothing like one that can hold at a partial capacity — and that one difference is what drives comfort, efficiency, and cost apart.
A building's cooling load is almost never a flat number — it rises through the morning, peaks in the mid-afternoon, and falls off toward evening, tracking outdoor temperature, sun angle, and occupancy. The question compressor staging answers is simple: how many capacity levels does the equipment have available to match that moving target? A single-stage compressor has exactly two: 100% or 0%. A two-stage compressor has three: 0%, a low step (typically 60–70% capacity), and 100%. A variable-speed (inverter-driven) compressor can hold almost any capacity along a continuous range, often from roughly 25% up to 100%. Same load curve, three very different ways of chasing it.