Since I am not certain if your question refers to immaterial vs. material benefits, I will attempt to respond to both options.
I have been observing Reiki in action for about a decade during my work at an inpatient hospice unit as a medical doctor. The observational evidence of the positive effects of Reiki and other “alternative” modalities have left a lasting impression on me, to the point that I have learned Reiki myself and have been actively practicing it since 2013, in addition to my medical practice. I do not have a scientific explanation of how Reiki works, but I continue seeing impressive results with Reiki on a daily basis.
So to answer the immaterial side of you question, I can tell you that those people, who have learned Reiki and are practicing it, are benefiting others by helping them on a mind-body level with this impressive healing art.
In addition, learning and practicing Reiki has a profound positive impact not only on the receiver of Reiki, but also on the practitioner himself or herself. For example, since I’ve learned Reiki, I am a better, kinder person. I am more relaxed and able to deal with stress a lot better. I worry less and I’ve become a lot more open-minded. Reiki has allowed me to let go of the ego-fueled directions in life, and has helped me focus on what’s really important instead. Learning Reiki has allowed me to take a path less travelled, but also the path, where I can be more true to who I am and to who I want to be, the best version of myself.
As far as the financial benefits, as with anything in life, I am sure that there are people, who may be using Reiki for financial gain. For example, I’ve seen online Reiki courses that offer Reiki mastership after a few-hours-long training. This can only be viewed as either a misunderstanding on the part of the person who is offering this type of online class (hopefully), or as a money-making operation, since Reiki is a hands-on healing art, and Reiki training includes a process that cannot be performed virtually.
With that said, we don’t have to let a few ‘bad apples’ spoil the whole batch. The vast majority of people who learn Reiki, offer it relatively cheaply and often for free. Reiki is a calling, and although many Reiki practitioners can make a living doing Reiki, overall, the majority are certainly not doing it just to make money, but rather to help others.