The first is PSD file compression artifact, which can quickly reduce the size of PSD file. Second, batch design files of PS layers, and cleaning unnecessary layers is also an effective way to reduce the size of design files.

Smaller PSD provides many useful scripts and functions to reduce the size of PSD files. It handles all layers, so you don't have to manually select anything. This panel can reduce/delete invisible layers and pixels, flatten or rasterize layers, apply masks, replace placeholder images with frames, and so on.