I've been adding notes to the SNDB for long enough to know that almost all inserts are tough to come by. However, they've been discovered typically in UNC and that's what most collectors are expecting to collect/keep unless they're a much less common variety (think SNR or the tough sheet replacements that show high BV). So for inserts that are VF and above (and special numbers with no detractions:tears/ink, etc) you may wish to hold onto them and then replace them with a better find if you come across one, or just get rid of it in the future (when needing the cash, etc) after its been established how (un)common the insert is. This is all up to you of course, but that's sort of how I usually go about saving and relinquishing my less common finds.