Hi all, I came across this circuit in websearch. i understood the operation but i didnt understand the need of diodes ? Could some one please explain.

https://drive.google.com/open?id=1T7MP6Tk83cLQXzGv23hpdeMoc0DmA_zt

 

That is a motor limit switch circuit, with bypass diodes for when the supply is reversed to make it run in reverse.

 

Think about it.
When the limit switch opens, what is the current path to start the motor in the reverse direction.

 

As already posted, it is an old trick to enable just two conductors out to the motor with the extreme limit switches in series.
Max.