Those brass inserts need to be epoxied into wherever you plan to use them. But they do add useless weight.

The only sensible use is to hold heavy objects with small bolts. If you're going to use large nylon bolts, they're going to be big. If they're big, CA hardened wood will hold whatever the nylon can hold. If they're small, CA hardened wood (if it's thick enough) will still probably hold whatever the nylon bolts can hold.