Soak Testing also known as Endurance Testing is performed to determine if the application under test can sustain the continuous loads.
Soak testing, non-functional testing involves examining the system if it can withstand a huge load for a longer period of time and there by measuring the system's reaction parameters.
Serious memory leaks that would eventually result in application or Operating System crash
Failure to close connections between the layers of the system could stall some or all modules of the system.
Failure to close database connections under some conditions might result in the complete system crash.
Gradual degradation of response time of the system as the application becomes less efficient as a result of prolonged test.
A system may behave as expected when tested for about 2 hours but when the same system is tested for 5 hours or even more than that, the problems such as memory leaks cause the system to fail or behave randomly or even the application might crash.