I found that sometimes I struggled to use my syns each day so I would end up eating something with syns, such as a chocolate bar, toast, crackers etc. just to get them in. However, this didn't feel right as I was eating for the sake of eating, rather than eating to feel satisfied, which I think slowed my losses. After a while I stopped doing that and instead used my syns on things in my main meals, such as ketchup, olive oil, salad dressing, croutons or nuts in salads etc. and I found that this had a huge effect on my losses, which went from 0.5 - 1 lbs per week to 2 lbs or more per week.
I think using them on things like chocolate etc. is absolutely fine as this is what they're for after all. However, SW is about being able to eat until you're satisfied so if you're already feeling satisfied when you eat chocolate (or whatever it is you're using the syns on), it may slow things down a little more than if you ate your syns as part of a main meal, at which time you're probably hungry. Maybe ask yourself if you're actually hungry before eating your syns or if you're just eating them because you're bored or think you need to because you haven't had any today. I'm a boredom eater myself, which is partly why I'm the weight that I am and it's a very difficult habit to break, though I'm working hard on it now to try to kick my sweet tooth for good!