For the most of we absolutely love training the feeling of knowing you've hit an all time PB or beat the log book by a couple reps gives an insane feeling and the concept of keeping that continual progression is what causes you to go back for more. I certainly know that feeling but with every good comes a bad so to say, and with continual progression comes the equally possible plateaus, fatigue and de motivation too.
When we train there is a lot more going on that meets the eye besides just lifting things up and then down again or getting a pump, within any muscular movement the aim it to cause a hypertrophy response which we do this by creating mechanical tension and causing the actual fibres to tear and repair back stronger as a brief description.
A deload phase is a type of training in which we reduce the Total loading within workouts in order to provide a state of rest for our bodies and create a window to bounce back with increased strength coming out.
The main signs of knowing when to deload are completely individual but a common one would be fatigue if you are consistently going into workouts feeling sore aching and unable to do certain movements then that would be a good opportunity to deload because by doing so you are still training however by reducing the load and taking a step back your CNS will surge in recovery meaning when you go back to normal training you are better rested and able to load up again.
Motivation would be another key sign for a deload because we know for the vast majority a clear vision and healthy mindset is needed to workout optimally therefore if toy are feeling un motivated this will likely cause a un productive session and be Half assed. By deloading with this in mind we are taking the mental pressures in sessions such as beating the log book and continual progression and further focusing on reducing the load on sessions to allow the mind to relax and recover better for when you approach the end of the phase.
Towards the back end of a cut would be completely individual and by no means instructed but In my opinion towards the back end of a cut could be optimal as it means when calories are at the lowest we consider the previous points of fatigue and motivation we would deload then exit this phase when we increase calories to go into a surplus this will not only rest your body but also lead to a huge jump in progression as you are fully rested and fuelled with increased calories.