New user Qs re preview and adjustment files

I have 2 questions:

First, when I delete an image from catalog or disk, C1 does not delete either the preview file nor the 'Capture One Mask' adjustment file. Is this expected behavior?

One way I am dealing with this is (without explaining my whole flow) to generate preview files that are the minimum size. So far I have not noticed any speed reduction, so I am wondering exactly what the preview files are used for when you are working online.

It could be that they are not making a noticeable difference because I only have ~20MP cameras and a fast enough machine with the images on a local SSD. I guess C1 is generating it's own 8bit on-the-fly preview as well - it needs to to preview at 100% anyway. But I'm wondering if there is something else I am missing - except the offline edit capability.

Thanks,

Ed.