I think it depends who you are.
I used to have a brilliant diet, then due to some awful personal problems I basically ate and drank my emotions. Now I'm in a better head space, about 3 stone overweight and I've lost my way. I'm exhausted after living through everything I did.
So, against everything I believe in, I've been doing sliming world (from an old book/pdf I found on pinterest, I can't afford to pay for it). I bloody hate quark, sweetner gives me headaches, and I wouldn't touch muller lights with a barge pole.
So why am I doing it? It gave me an easy way to be accountable. I follow it loosely, following the principles of trying to replace my mid-morning chocolate bar with fruit, and my mid aftenroon bag of crisps with something more fruit/veg based, my evening chocolate is there, but perhaps not a massive bowl of dairy milk, and I'm still having a g&t and/or a glass of wine. Just not a bottle. I still have a croissant at the weekend, and a full on sunday roast (yorkshire puddings made properly not with bloody porridge oats)
I knew everything, I just needed the 'syns' side of things to keep my mind in check to hopefully change my lifestyle back to what it I was before. It probably doesn't make any sense? I loathe myself for joining 'the cult' as I always called it, but actually I'm feeling a lot better and remembering what it was to cook a meal from scratch and not jsut stick some oven chips in.
I'm warbling. basically, if you follow it to replace bad habits (etc not always turning to carbs and chocolate) it's probably more sustainable? I don't know. I'm not massively thinner yet, and I had a wobble a few weeks ago when I was getting my head around it, but the more I do it, the healthier I feel. Mainly because i'm having a lot more fruit and veg and a lot less salt and alcohol!
OH. Also, I'm not going for the massive 7lbs in one week weight loss, because I think when it comes off that quickly, it probably isn't sustainable, I have a friend who does WW and she basically starves herself, then when she reaches target weight binges, then starves herself, then binges. Which is why I can't see me counting the points.
SORRY. I'll go now. Hope I've made some sort of sense!