Index related DMVs and DMFs - sys.dm_db_index_usage_stats:

Examining statistics of indexes is useful for optimizing the performance of queries. Statistics help us determine the usage and worth of indexes. There are many different methods to determine their usability; , which gives core statistics of indexes. The first article in the index-related DMVs and DMFs series discussed the output of sys.dm_db_index_physical_stats, while this, the second of the series, will explore some output columns of the sys.dm_db_index_usage_stats DMV.

And some indexes are taking up a ton of space, only to have no queries actually care about the information, so useless...