It is very very annoying the feature that prevents accessing from more than 3 devices. The problem is not only  the limit of sessions but rather when you reach the limit of devices. 

When I reset my computer and clear the catche and history from my browser the system did not allow me to enter into pipedrive. ( I only have 1 PC, 1 Mobile and 1 Tablet)

When "the limit is reach" there is no option to access the device settings and logout, because the system does not allow you to enter. This is the third time that this is happening to me, this time a have a very quick answer from someone of the support team.  The problem with this is that you are depending on someone else to reset the devices. 
 

What happens if the other device is lost or broken and I could not close the session?

This is a clear example. This happened minutes ago when the support team reset the sessions. I am using only one computer to enter the system and it is thinking that I have 2 sessions. 

Also, your mobile app (The one on the cell phone) does not let you access your device settings to reset the limit.