When to compress, when to resize, and when to do both
Compression reduces file size by lowering quality or optimizing encoding. Resize reduces pixel dimensions. Both cut file size, but differently. Use resize when dimensions are too large for your layout (e.g., 4000px for an 800px column). Use compression when dimensions are fine but file size is too big. For best results, do both: resize to match display size, then compress to 80–85% quality.
Resize: Wrong dimensions (hero, thumbnail, social). Compress: Right dimensions, bloated file. Both: Large image for web—resize first, then compress.