I think the dangers of under eating on MJ is that you risk veering perilously close to Eating Disorder territory. It can be a heady experience, being able to ignore food and I think most people dice around this in the first few weeks. Fortunately over-strong appetite suppression wears off and naturally settles down by about months 4-5.
Just in the same way that any thread on AIBU about food and portion sizes brings out pages and pages of insane competitive teeny tinies shrilling on about how little they eat, threads here on this board and tiktok etc etc tend to do the same. Unfortunately this gives the impression that this is normal and necessary. It is neither.
The amazing, great, wonderful thing about WLI is that you can eat normally. Like a normal person! There is no need to eat 500 or 800 calories a day or live off a cereal bar and a shitty protein drink. You can have delicious properly calorie counted meals (packed with seeds and nuts if you wish!), and you can eat them and really enjoy them and just allow the drug to work by ensuring that you will not feel the urge to eat too much and that you will feel satisfied afterwards.
Most people find that they start to crave healthier foodstuffs and fruit & veg etc and to be repulsed by UPFs and diet coke and Kentucky and chocolate and all the stuff that previously would be considered a 'treat'.
Regarding gaining weight again when you stop - well yes, all the studies about any diets shows that most people will regain the weight within 5 years. I don't know if it is a fact, but it completely makes sense to me that if you have starved and malnourished yourself through your WLI journey, then your body is going to fight back - and win - very, very quickly after stopping. Your body will be ravenous.
So better to take it slow and work with your body rather than fighting it. Why not take a few extra months and lose the weight gently and steadily without stressing and damaging the body, as a pp has described.
There is no need to undereat or do extreme low calories. WLI can hand you back control over eating, both in quantity and quality. It makes sense not to abuse that.