The answer to this question separates good coaches from not-so-good coaches. I like to think about feedback once in a while to remind myself of good habits.
If /when you provide feedback you have to consider the timeliness, usefulness and purpose of what you say.
One thing is for sure: if your feedback is not intended to make the player better then keep it to yourself. A player knows if he caused a goal against. So instead of yelling "You caused that goal!" be a coach and have him replay in his head what he might try next time. The former is meant to make you feel better, the latter will help the player.
When used properly, feedback not only makes your players better, it also serves as motivation for them to be better. There is not a player in this world who doesn't appreciate useful information and respect. If the feedback creates an environment of collaboration to make the player better the results will be noticeable and rewarding.
Let the players play. Choose your moments to coach and make sure the moments are timely. If you over-coach and keep stopping the play, your voice turns into background noise and you kill the flow of the session.
Know your audience. Is your tone of voice and content of your feedback appropriate? Are you using feedback suitable for a U17 professional academy player on a U16 recreational player? Are you coaching teenagers in a co-ed camp with potential for embarrassment? Are you talking to the best player on your team or a weaker player looking for a boost in confidence?
What mood are you in? One session last year I was in a sour mood and when I realized I was getting a little too sarcastic I set up a small sided game, sat on the side next to a dad and cheered. I stopped coaching, but the players kept playing and enjoyed themselves. Your players don't care if you had a bad day at work, they came to play and enjoy themselves, regardless of the level.
When you are planning your session make sure you list your coaching points. Your feedback should be based around your coaching points and keep the intended theme of your session focused.
Your points should be clear, concise and informative. No babbling on or recounting what your team did in the 1989 men's league final. Say what you need to say and get out. (FYI. We lost the 1989 men's league final. I don't want to talk about it.)
Coach what you see. Give feedback on what you see and what happens. Don't make things up for the sake of coaching. The kids want to play. If they are not making mistakes, let them play.
Observe/Identify/Demonstrate/Rehearse/Restart. When you see something that needs to be addressed stop the play right there and then. Step in, demonstrate how they should do it, let them try it themselves with no pressure, then restart the game.
No jargon. Use the proper language associated with the task and age group. No clichés or inside jokes. The feedback must be useful to everybody if the entire team is the audience.
Restart methods. If it's a drill, that's easy... just start the drill over. If you're in a game what you need to get the ball back to that player. Get everybody back in their positions when you stopped. Let's say, for example, John on the red team is the player you wanted to correct when you stopped the play. Tell the group nobody moves until John touches the ball, then pass the ball to his opponent and he will pass the ball to John and the game begins on John's first touch.
No need to always stop. Feedback does not always have to be saved for stoppages. You can quietly cruise the play area and pass on information "John, make sure you open up when the ball comes, Lou is open all the time" or "Tara, remember to use your keeper as support if you are forced to turn with the ball".
Timely and appropriate feedback is an art form that takes practice. If you need help with it, find a licensed coach for guidance. Most of what we were assessed on revolves around the timeliness, delivery and usefulness of our information.