In my opinion it’s a hugely valuable feature and worth the space. There are mechanisms available to reduce the amount of space required by the thumbnails.
When Settings → Library → Generate video preview thumbnails is set to as a scheduled task and when media is added, analyzing an individual media item will trigger thumbnail generation for just that item.
If you only want to create thumbnails for individual items, you can temporarily set it that way, Analyze an item, watch for it to begin, and then set it back to never.
