You should always feel soreness when you train...

"Working out"is totally different from "training".

Now that this is out of the way,when "training",the specific goal becomes the vision.

Which is when soreness comes into play.

You do more effective sets and reps which breaks down the fibers more than just "working out". There is a finish line.

An ultimate goal. So if you do not feel any soreness after training,chances are,you have not broken down,or gotten enough blood into the muscles to reach the goal.

Thus adjustments must be made....