If you create a custom table that includes any Aha record field, that table gives you a tag-like ability to see and link associated Aha records. However, when looking at an Aha record, it gives no indication that there's a related custom table entry that tagged it.
For example, if a custom table includes a Features field, when you are adding an entry to that table it'll show all the Features as potential tags. Pick a feature and it's added as a tag. When you click to a feature that you've tagged, it makes no reference back to the custom table entry where you tagged it.
My company has a custom record to keep track of notes from conversations with users. We link this custom record to our standard Aha records (particularly Initiatives) so that we can keep track of which user has left feedback regarding one of our projects.
Since we can't see the linked custom records in the initiative, we aren't able to link back to the user feedback from a particular initiative, making the ability to link mostly useless.