Investing in domains is basically the same as investing in real estate, shares or antiquities
An asset is different, but overall it is the same. You as a domain investor or businessman buy a domain because sooner or later you want to sell it for profit or you expect that it will generate a passive income during the time you own it. You can get two types of income from domain selling: capital income and passive income. The capital income is from the sale of domain and the passive income is from domain rental.
Nowadays, the major part of high-quality domains are already occupied. The good news is that many of them do not have developed websites and these domains are for sale. There are several good reasons why to invest money in domains. Perhaps, the absolute advantage is that it is a lucrative business and for most people it is also an accessible method how to increase their money in value. It is still possible to buy a good domain for a registration fee and sell it even for multiple profit within a short period of time. Myself, I have sold a few domains via website domainfs.com for a few thousand percent profit.
Every single domain is unique and therefore it has also its own value. There is only one domain domainfs.com or rivalengine.com, etc. One word domains are the best and the most sought after. You can buy a domain that is currently not very interesting, but this can change in the course of time and you can sell it for a multiple profit.