Microsoft Access subdatasheets are a valuable way to see one-to-many relationships from a table's datasheet view. It requires no programming to see the related records and is very compact display of subdatasheets with varying number of records.
However, if you do not want this, you may be suffering a performance penalty.
By default, the Subdatasheet Name property for tables is set to [Auto]. When the table is opened, the datasheet automatically looks for, and includes, a subdatasheet based on its table relationships. If you want this feature, it would be better to explicitly specify the subdatasheet table.
If you do not want this feature, setting this property to [None] significantly improves performance, especially over a network, when you open the table. It also impacts references to the table from queries, forms, and reports.
To change this property, put the table in design mode and change its Subdatasheet Name property from [Auto] to [None]: