A module is composed of different parts called elements, when these elements perform logically similar operations then this cohesiveness is called logical cohesion.
Flag determines which Operation to Perform :
This cohesion to some extent needs grouping Functionality. It grouped function on the base of technical characteristics, not for the purpose of functional properties. Flag or label determines which functionality this time to implement. In this cohesion Modules are logically linked and intertwined.
Why Logical Cohesion is bad
The modules are linked and create ambiguity; multiple functionality performed by the modules. It is difficult to understand.
Reusability of the code is very difficult if it has logical cohesion in it.
The Interface of the product is difficult to understand, it contains large number of data pieces.
One object performed multiple functions, like same object taking input, after processing showing output. This all functionality is performed by one object because modules or data is logically linked.