orbic,
As you use your database, Access needs some "scratchpad" space to do
its work. Designing forms, running queries and creating recordsets are
actions that require Access to "get more space".
Unfortunately Access does not reuse this space and over time your database
will "bloat".
The compact operation just copies all of your database objects into a new
database, and if successful, renames it so that it is transparent to you.
You can set it to compact on close if you want.
Use the search facility here and look for "bloat" and "compact" and you
will find more info.
Wayne