YCbCr is the colour format that every video codec actually works in internally — Netflix, YouTube, Zoom, broadcast TV, your phone's camera. Instead of storing each pixel as red/green/blue (rgb), YCbCr stores it as one brightness value (Y) and two colour difference values (Cb and Cr). It carries the same information, just rearranged.
Why bother? Two reasons that combine into a huge compression win. First, the brightness/colour split matches how human vision works — we're much more sensitive to brightness changes than to colour changes. Second, that split lets codecs use chroma-subsampling to cut colour resolution in half (or by 75 %) without you noticing — something that's impossible to do cleanly in RGB. The result: starting in YCbCr instead of RGB saves around half the raw data before any further compression even kicks in.
You'll see "YUV" and "YCbCr" used interchangeably in casual writing. Strictly, YUV is the analog version (old TV broadcasts) and YCbCr is the digital one — but in modern video work it's the same thing. What you should remember: cameras and screens think in RGB, codecs think in YCbCr, and the conversion between them is automatic and lossless if the right color-space (BT.709, BT.2020) is tagged on the file. You don't make decisions about YCbCr; you make decisions about chroma subsampling, bit depth and colour space, which are the visible knobs on top of it.
