Whats the difference? Muscles can be tight for a variety of reasons. That will be a different post unto itself. But often times the quality is junk. Knotted, tight, tender are words that may describe it. When the muscle is like this it won't have the same contractile properties as healthy tissue. It won't act optimally when you need it to. It may actually be the source of your pain. Stretching won't work. Here's an analogy. Imagine a knot in a rubbber band. It's not at its optimal length. If you stretch it the knot won't come out. In fact it will get tighter! So you have to get the knot out if you want full function of the rubber band (the muscle).
How do you get it out? Foam rolling is a great inexpensive option. Rolling on a tennis or lacrosse ball is another great tool to get the smaller more precise muscles. Active Release Technique from a trained practitioner is a great option as well. So spend at least 10 minutes after each workout training regeneration. If you don't have time to warm up before the workout and time to recover from it afterwards, you don't have time to workout. I often have athletes just do the regeneration work if time is an issue or it is an off day. I know if the tissue quality is there, the next workouts will be tremendous. So get to work.