You really don't want to give some random SaaS tool full permission on your production web origin.
If I'm Example Ltd. and my customers are trusting me to keep their data on example.com safe, and I use example.blog for my blog hosted by Jimbo's Blogging Service, I don't need to worry about Jimbo or his employees or hackers targeting my blog getting access to example.com's cookies, local storage, etc.
Cf. It's really hard—in some cases impossible, without use of the Public Suffix List[0]—to completely wall off blog.example.com from example.com.