There is no need for database indexes in most cases, as the database can simply use a linear search to find the desired information. However, when dealing with large datasets or frequently accessed data, database indexes can significantly improve performance by allowing the database to quickly locate and retrieve specific records. Indexes are created on columns or fields that are used most frequently in queries, reducing the number of writes required to update the index. The main difference between relational and NoSQL databases lies in how indexing is implemented, with relational databases relying on column-based indexes and NoSQL databases often using more flexible and customizable indexing methods.