As stated previously, session management allows the application to track user activity and validate authorization conditions without requiring the user to submit their credentials every time a request is made. This means that if session management is not properly done, a user may be able to access other users' information or execute actions beyond their privilege level, or an external attacker may gain access to a users' information and functionality.
Burp Sequencer is a statistical analysis tool that lets you collect a large amount of values, such as session IDs, and perform calculations on them to evaluate if they are being randomly generated, or maybe just obfuscated or encoded. This is useful when dealing with complex session cookies, as it gives you an idea of how the cookies are being generated and if there is some way of attacking or predicting them.
To use Burp Sequencer...