I-140 Pending and Change of employment.

[RaviGanesh]

My I-140 has been filed in July 2016 and is in pending status. I want to switch to a new employer. Do I need to change the employer only after getting my I-140 approved ? 

Please let me know what is the advantage of doing that ? Do I need to stick to my current employer for some time before moving to new employer with approved I-140, or can I move the new employer as soon as I get the I-140 approval ?

Please help me on this. 

Thank you.