Indexes slow down data changes.
SQL Server doesn’t have the concept of asynchronous indexes – copies of the data that it could update later when it’s bored. It has to keep every nonclustered index up to date, every single time you change data, like a delete/update/insert.
Mo’ indexes, mo’ problems.
That’s why in my Mastering Index Tuning class, I start my D.E.A.T.H. Method with Deduping and Eliminating indexes that aren’t getting used. You wanna get rid of the dead weight that’s only slowing you down, and it’s especially important before adding more indexes.
The safest indexes to remove are