It took 12 months of badgering before my wife finally agreed to go to marriage therapy. And then another 2 months before she stopped vetoing the therapists I proposed (They have the word 'sex' in their bio? vetoed! You can probably guess how many marriage therapists don't have sex anywhere on their webpage).
Finally, the pages of notes I had written for myself about things I wanted to discuss with a 3rd party present so she didn't flip out (she has very poor emotional control) as soon as I would bring up certain issues. Except that we never got past the first line.
A typical 60 minute session would consist of 5 minutes of introductory chitchat, 50 minutes of her saying that everything reminds her of things I once did wrong in the past, that she knows it is irrational but she can't help not forgiving me (or anyone else for that matter) or wanting to try in the relationship. Maybe 5 minutes somewhere in there where my thoughts might be relevant to the discussion - I honestly felt like a bystander at her own personal therapy session. The worst aspect was that at times I felt like even the therapist was grasping for straws, she was just offering nothing to work with (lots of "that's just the way I feel and I can't change it") and thought that just turning up was evidence that she was meeting me half way.
After ten weeks of this, with every single week the same outcome from her ("I'm not sure I want to try"). So I persevere, because marriage vows, kids, hope triumphing over experience etc. Then she decides that the therapist is too far away and too hard to get to (um yeah, that's what I said at the very start when she knocked back all my choices and chose this one). So she cancelled the sessions "to find someone closer". That was 2 months ago and despite my weekly reminders she hasn't made any new inquiries.
So did anything good come of it? There was a session where the therapist got me to say things from her perspective -- which she was shocked to find was in fact exactly what she felt. That lasted about a week until it went back to "you just don't understand me" again. She also acknowledged that 1 night per year is probably not a sustainable amount of time for a couple to spend together and that she would organise something (there's always a reason why the things I organise are "just won't work"). Maybe one day she'll get around to it, but she acknowledged it so ... can we count that as progress?
TLDR: Just one data point, but I found therapy utterly useless. If you have to drag your partner along then you're already set up for failure.