In my opinion, the latter. Some people may tell you differently, but it is my belief that if you're doing a weight loss spell, you should do it for motivation, to help you exercise and eat well.
I think weight loss spells may be able to affect actual weight a bit, but not without effort (ie, a weight loss spell would make it easier for you to lose weight, but only coupled with healthy eating and working out).
i feel they're motivators. i have a weight loss aid i got from a friend back in high school. it lasts for about a month, and all it does is reduce cravings for junk food, and when you do eat them, normally, you'll feel pain [i got headaches, my friend felt light headed, another friend said they felt nauseous] a spell will not fix poor eating habits permanently or make you lose 50 pounds in a night, but it will help give you the extra boost you need to do the work. spells are meant to bring desired change [or set things on the right path for the change] a job spell won't have an employer knock on your door and hire you despite not passing out any applications, but they still work by helping you find jobs, get interviews, and perhaps let the employer look favourably upon you in the interview. you still need to put in the effort however.
Depends on what you mean by weight loss spell. Every spell is different, as it is something created individually.
Obviously if you do not put energy behind something it will not work. The idea of a spell is to put energy, intent, will and focus behind something. You could create a spell to help stave off cravings. You could create a stinging nettle tincture (always consult your physician), recite a prayer and enhance your bodies metabolism. You could dry scrub your body in front of a mirror while visualizing your desired weight loss manifesting. And so on..
How a spell works depends on what is done and why, along with the actual energy put for into it. One could say it is meant to bolster your efforts and that you must put forth the diet and exercise to achieve results. No one can tell you for certain though. Believe! Just don't be delirious lol