Yes, at first ANRs seem like a dream come true to newcomers and they are eager to begin one, but ANRs can be very demanding and challenging for people that aren't committed to the idea or who rush into one; people that aren't ready for that kind of commitment or who have that kind of patience usually wind up extremely disappointed.
The insights I am addressing now only came from personal experience, that's the only reason I know what I do. A lot of lactation seekers are in it for the erotic gratification (and yes, while there is plenty to be had) there's nothing wrong with that (everyone has a kink) if it's a one time experience they wish (and the other party is well aware of it) but being smart enough (like you, dear reader) to realize it's something they want to sustain, is another thing entirely.
ANR can be a pretty heavy topic because of it's emotional liability. For both partners involved the relationship becomes both more and less emotionally stable, more stable because it really does something amazing to the bond you share; the hormone oxytocin (aka the cuddle hormone) engenders immense feelings of loyalty and love for to the other person. It creates closer intimacy, more tenderness, and warm fuzzy feelings. Plus, from a woman's perspective, the femininity is overwhelming; knowing you could save a life with your breasts.
For me, part of breastfeeding another person is based in the desire to bring comfort. Being the altruist that I am, the idea of nurturing someone in a way that no one else in their life does, them depending on me for something only I can provide, and gaining sustenance and nourishment from me as nature intended the breast to function; those ideas are all very gratifying and I think it's why I love nursing so much. It's a way to calm anxiety, both mine and another person's, and the worries of everyday life seem to evaporate even if only for a short while. It's such an amazing and empowering thing to be able to provide that kind of comfort and solace for someone else.
It's also emotionally less stable because while ANR is a healthy co-dependence, it's still a co-dependence, and if the breasts are not emptied often enough they become painful and sore, and that can cause major resentment between partners, and hell hath no fury. If her partner keeps putting her off and only empties her breasts sporadically with no routine, and she's left to do all the work herself, it can feel a lot like she's carrying the entire weight of the ANR (doing all the work and only keeping up the supply for convenience) when every relationship should have equality.
Conversely, for the person being breastfed if their partner isn't feeling up to it, is sore, etc, then it can also cause resentment because nursing is a time period in which both partners experience a release of anxiety (the oxytocin in the blood stream i.e. the cuddle hormone) and warm fuzzy feelings. And if the lactating female's heart is just not passionate about it, is spotty on keeping up an expression schedule, and forgets often, it can make the nursing party feel neglected, ignored, not cared enough for. Really it's a whole mess for both parties.
People often ask me, "Is an ANR bad or good emotionally?" Based on everything I just addressed I'd say it's emotionally different, not necessarily "bad" or "good."
So, if you're seriously considering an ANR, please do consider these emotional issues as well. It's not a commitment to be taken lightly, and both partners have to be in it to win it. Some good resources for more information on ANR are: