Bitmap index provides the same functionality as a regular index even though it uses a different representation internally. If the number of different key values is small, then bitmap indexes are very space efficient.

Bitmap indexes are good for low cardinality columns have a small number of distinct values
e.g. Gender or Marital Status

Bitmap indexes can dramatically improve the performance of ad hoc queries.

These indexes are primarily intended for decision support in data warehousing applications where users typically query the data rather than update it.

Therefore, bitmap indexing is of great benefit to data warehousing applications.

Update - For some more information on Bitmap index, Refer here

Hope that helps --