- Well the person who set that up stopped responding, isn't there another way to get this going? - I've added all the record in what do you mean they don't match? - I don't even know what DNS is, why is this necessary? - I added in the record but the system didn't take one of them because it started with an underscore and they said that was invalid. - We just switched websites to WIX, why is our shop page not loading, is your system down? - Will this break my email, I don't want it to break my email. - Here is my login, just go in and change what you need.
So in all, it's not just $10, it's a significant investment in time and resources to do this "simple" change that until this point did not have any downside. Hindsight is like that every time.
The best reason not to do full domains is the risk of bad actors re-registering domains you release, as schroeding points out in another reply.
Client.SaaSdomain.tld
not
Shop.clientdomain.tld
If you’re setting up your service as a subdomain off the client domain, you won’t face the risk that one customer will get your entire service domain blocked (since it’s the customers domain).
They already have to do that, only currently they have to put it into customername.shop-saas.com, not customername-shop.com, or even shop.customername.com.
Or here is our 75/year plan which includes a domain to ensure you don't run into problems with social media
Instead of client.your domain.tld, register client-your domain.tld. This would prevent one bad actor from nuking your whole business.
Yes it has a cost, but it’s like $10 a year for a new domain, which I bet pales in comparison to other direct costs of running a SaaS.