What is the difference between Single Logical Table Source and Multiple Logical Table Sources?

Below is the difference between "Single Table Source" and "Multiple Logical Table Sources" in OBIEE
If a logical table in BMM layer has only one table used as a source table then it is called as Single Logical Table Source and in case the logical table in BMM layer has used more than one tables as the source to it then it is called as Multiple Logical Table Sources.

For example -
Fact table has Multiple Logical Table as (in general) sources used in Fact tables come from different - different physical tables.

What is the use of LTS (Logical Table Source) in OBIEE

Logical table sources define the mappings from a single logical table to one or more physical tables. A logical table contains one or more logical table source. The mapping between physical columns and logical columns are done in this element.
The definition of the logical table source is used:

• to specify transformations/calculations (in the column mapping tab),
• to enable aggregate navigation and fragmentation (in the content tab)

The Content tab of the Logical Table Source is used to define :

• any aggregate table content definitions (specify the grain of the physical tables),
• fragmented table definitions for the source,
• and WHERE clauses (if you want to limit the number of rows returned).