Yes, it helps. Because change happens when the pain of staying in the same situation is greater than the love in a relationship. Just like a proper medical treatment is essential for medical distress, a psychological treatment like couples counseling or therapy is needed to diagnose a "sick" relationship. Marriage retreats are recommended for a failing relationship, marital distress or a couple in crisis.
Of course couple therapy works in real life, but it is not a treatment to be applied to a passive patient who just sits and waits for healing. Couple therapy works very well when both parties make a commitment to engage fully in the process. If one person in the relationship already has one foot out the door, so to speak, and has decided they want to split up, couples therapy won’t help unless that person makes a commitment to stay in the relationship and work on the problems. It isn’t easy to look at ourselves deeply. But connecting with a loving partner in this life is well worth the trouble.