I think making resolutions at New Year puts pressure on people to achieve them at what might not be the most opportune moment.
I feel it is much better to resolve to do/not do something when you are in a "good place" emotionally. To try and give something up, for instance, when you're feeling stressed or depressed may well lead to failure and reinforce feelings of powerlessness.
Also I think some people tend to set themselves targets that are too high. For instance, why not moderate a particular behaviour rather than try to eliminate it?