This article points out some of the pain associated with index maintenance. It should also point out that ALL indexes on a table suffer from the same issue. If your 20 column table has 7 indexes, then the suggestions should be applied 7x.
It is conventional wisdom that indexes are absolutely essential for any relational table of at least reasonable size (e.g. thousands of rows) and is accessed more often than daily. Indexes can be a pain to create and maintain; but can greatly speed up queries and primary key validations. The pain mostly comes from having to figure out what indexes to create and how often to maintain them, rather than doing the actual thing.
Indexes also have a performance penalty for any table updates. Creating new rows, updating existing rows, or deleting rows all require updates to each index.
But are indexes really required? I am creating a new kind of general purpose data management system (a kind of object store) called Didgets. The tagging mechanism that I invented to allow tags to be attached to each data object, are key-value stores that essentially form a set of columnar stores.
I found that these columnar stores could also be used to create regular relational database tables. The data is structured such that indexes are not needed. All the tests that I have run (up to a thousand columns with over 100 million rows), show that query speeds are equal to, or better than other database systems that are well indexed.
The system is still under development, so it is still missing some key features that would make it a drop-in replacement for other databases; but it proves that it is possible to structure relational data such that query speeds can be optimal without needing separate indexing structures that have to be maintained.