Database Maintenance is an important task for any Database Administrator..
When you remove objects (forms, reports) and data from the database MS-Access marks them as no longer required but doesn't actually free up the space on the hard drive.
Also, when you add data to a table it maintains indexes to speed up sorting and searching. When you remove records in a table it updates the indexes by marking for deletion any that are removed or if you add a record it creates links to the other indexes.
So that you are not waiting while these operations are performed, access does not remove the objects or data but marks them as no longer required. This means that your database can have a lot of unnecessary objects or data, so it is good to regularly run a tool to remove these unnecessary objects or data.
To do this Access provides a "Pack and Re-index" tool, and this should be run regularly to keep the size of the database on the disk small and improve the performance.