Some anti-cultists like to post a list of "post-cult syndromes", the weakness of which has been discussed by Monica Pignotti and Lema Nal.
However, why not post lists of strengths too? (Bearing the same limitation that these are not necessarily caused by cult membership).
I can see a few positive aspects.
I was interested to read recently that most high profile defectors have done rather well in re-integrating society, in spite of having spent 20-35 years in Scientology and having no formal high-level education. I have seen that with myself and my friends as well. I think it has to do partly with some of the useful things we learn while in such a group, but also because of the fact that (I believe) most "cult members" are bright people who join alternative groups because they see through the limits of society and are not satisfied with it. They are idealist-oriented people who seek something better.
The "cult experience" also provides one with a feeling of "having found what I was looking for", a feeling of engagement and belonging, of dedication for the common good, responsibility for the world we live in, etc... I think these are positive and somehow stay as inner qualities after one quits the group.
One also may experience states of heightened awareness. It gives them a taste of what true spiritual experiences might be. It is similar with drugs. In spite of the negative effects of drug, it can give one an idea of higher states of beings. Often, after getting rid of the negative influence of drugs, one will seek to experience the state back, but without the dependencies this time, and I think that's a good thing too.
Ethic - one's sense of ethic is strongly reinforced while in a cultic group. This may sounds strange and I will explain later, but this is in fact what happens. One becomes more aware of the consequences of wrong doing, of the energy balance in the universe and the reaction of one's own spiritual being to ego characteristics such as greed and cheating. After exiting the group, one may retain this sense of ethic, and I believe it makes for more honest and responsible citizens. Again, you could say that the sense of honesty was already present in the 'cult member' before, but I believe it is part of what makes him attracted to the group and that the group strenghten those qualities.
Now how come, if the above is true, that cultists are being cultic? Well, that's the irony of all cults, including anti-cult cults and political parties. They just do wrong in the belief that what they do is good! It's the whole dialectic of cultism and I am not going to go into that now.
Which brings me to the next positive aspect, not linked by one's belonging to a cult but, on the contrary, the process of going out. Going out from such an high level of personal involvement requires tremendous questioning and integrity to look. When you truly realize the limitations you have fallen into, which I refer to as the cultic mindset, then you can see it in other groups, and this may help you chose better next time around. By itself, it also is enlightening and one can learn a lot through this too. You realize the importance of never assuming, keeping yourself open to self-questioning (which makes you more humble, a spiritual quality), and the importance of free speech to avoid getting trapped in a closed group/cult mentality.
Of course, as I pointed out many times, not all ex-members learn from their exit in this way, and they on the contrary become involved in the very same mentality they were trapped while in the cult but on the other side, and doing really wrong things - all the while still believing they are doing good. This is just the next trap we need to learn, and once we can see that trap too, then, again, we really gain more positive insight, beneficial to our own evolution, and beneficial to society, because it makes for a less intolerant society, where individual members gain the courage to question the majority's assumptions and stand against mob mentality.
So, on the whole, I think the cult experience can be really positive too. It strengthen the good qualities in the individual and provide him with the taste of "something" our sclerotic society and religions usually are unable to provide. It further makes the person wiser as he exists the group, in that it makes him more aware of a variety of illusion one can fall into. Again, if the person is able to avoid or exit the anti-cult trap, it makes him/her more perceptive of yet more illusions.
These are a few positive things I can see, at first sight, about the "cult experience", and things that would be fitting for a positive list.