Let’s say, hypothetically, your company acquires another and fails to develop an integration plan. Can you develop a plan mid- or even post-integration? Can you correct errors or bad decisions after the fact? How long can you go before the damage of not effectively integration an acquired company is too great, in your opinion?
I think it depends on the function you are integrating. If left alone employees at the target company should know that they will integrate at some point, but just TBD on when that will be. Without communication and honesty into the plan / its development employees may become resentful and annoyed by the integration exercise.