Buffett's can be a good thing or a bad thing.
In relation to Slimming World, you want to avoid anything deep fried, covered in pastry, anything in a creamy sauce (carbonara, korma, tikka masala, etc.), the mexican stuff might not be too bad, although the taco shells and tortillas are synned, so is the guacamole and sour cream.
Sushi isn't too bad, the wok station might be ok - see if you can judge how much oil they use when they cook something for someone else
The pizza and fried chicken ones are ones to avoid though if you want to stick to low syn!
If it was me, I'd try to be sensible in looking at what's available, and what would be the worst choices (deep fried, pastry, tortillas, creamy tihngs) and then take my pick from those. I wouldn't decide to 'stuff it and eat everything in front of me' but I would try to enjoy the meal out and have fun, and then get straight back on plan the next day
Hopefully I've been of some use!!