Zip files take up less space on disk, which also means they’re more quickly read from disk. Since most things are I/O bound, the overhead in decompressing the packaging may be less than the overhead in reading a larger file from disk. Moreover, it’s likely that a single, small-ish zip file is stored sequentially on disk, while a collection of smaller files may be more spread out. On rotational media, this also increases read performance by cutting down the number of seeks. So you generally optimize your disk usage at the cost of some CPU time, which may dramatically improve your import and load times.