part files is what made WinRAR so popular with the piracy community. Especially back in the before times, when you were direct downloading and an internect hiccup would cause a download to fail/restart. Being able to download a thing in smaller parts, only having to restart smaller chunks instead of the whole, and then assembling the whole build as one.... that's what made WinRAR useful....

Compression was nice and all too, but self executing part assembly was the standout feature. Again, rendered useless when download managers are built into modern broswers. You can retry a direct download without having to restart the whole file.