To be perfectly honourest its a bit of both, since 2010 I have been wearing diapers/nappies on and off because I became partially incontinent through no choice of my own and I have a medical condition known as over active bladder syndrome.
And if I did not wear them I would have more embarrassing accidents and that's something I am trying to avoid at all costs, even if it makes me look and feel like an over-grown toddler at times.
So that's the needing part over next comes my choice to wear diapers mostly because of the comfort and relaxing feeling they provide me with but also for re connecting with my childhood when everything was more simple and innocent.
I tend to wear diapers when ever is practically available even for naps and sleeping st night, jusy like a real baby/toddler would do although mostly without the childish mentality expect when I choose to fully regress.
And whilst writing this I am wearing a pair of Tena Value adult diapers in the largest size as I cannot fit into the smaller one, even-though its only a couple of inches different to the ones I am in now.
However going back to the subject at hand I wear diapers/nappies virtually 24/7 and If I was invited to a diaper party I wouldn't say no as I would have fun without the un nessisary stigmas attached to being in these products.
Diapers are just another form of underwear and you shouldn't be made to feel embarrassed or ashamed to wear them.
I hope this helps awnser some of your questions.