[zzem]

I think the main advantage is the ease and speed of use for people who want a simple, business-card-like website or a holding/landing page.

The main disadvantage is that due to the UI/UX of domain control panels, managing anything more than a few paragraphs of text gets messy really quickly. But that could be actually an advantage, as the DNS is not particularly well suited to serve large amounts of data, and the app itself is meant for small and simple websites.

[coretx]

Let's be honest here. The main advantage is to make use of someone else his resources. Since it's potentially degrading critical infrastructure and increasing the cost of market entry: Unethical.

[zzem]

Sorry, but I don't understand your point. How is this "degrading critical infrastructure" and "increasing the cost of market entry"? It's also not using someone else's resources - DNS hosting is a web service like any other. You pay for it either as a part of domain registration/renewal cost (when DNS hosting is included in the registrar's offer) or separately (e.g., Route53 or "Advanced DNS" offerings).