Danger of Cascade top document's permissions to 3rd party sc

[scripteze]

The option under Advanced > Trusted: "Cascade top document's permissions to 3rd party scripts" has always been disabled by default. I guess it still is?
Recently, TorBrowser developers decided to enable it by default, beginning in TBB 3.6.4.
NoScript FAQ 5.6 explains the purpose, but I'm not sure about the potential pitfalls of enabling the option by default.
Aren't there some serious considerations for enabling that option?

5.6
Q: Why do I sometimes need to reiterate the (Temporarily) allow all on this page command twice or more on the same page? Doesn't "all" mean actually every single script?
A: For security reasons, "all on this page" means every script source which has already been detected on the page and shown in the NoScript menu: this way you can check in advance what you're whitelisting, even if you're doing it in a single move. This means, on the other hand, that if a script you've just allowed now tries to dynamically load another script from a different origin, not seen yet, this new load attempt will be blocked, so you're given a chance to choose whether allowing it or not. In other words, you need to reiterate Allow all on this page until no more "surprise" scripts surface after your command has been issued. If you believe this is too much security for your needs, you can switch on the Advanced|Trusted|Cascade top document's permissions to 3rd party scripts option, which will automatically allow all the (possibly nested) scripts on pages whose top document address is whitelisted.

First, the FAQ says this applies only to whitelisted sites. Which just means you've allowed scripts from a "trusted" site's domain.
This seems to imply that whitelisted sites (if one designates any) aren't susceptible to being compromised / hacked?
And ANY site you temporarily allow scripts on (just to make the basics work) becomes whitelisted, until it's revoked.

That doesn't mean you trust such sites enough to allow any & all 3rd party scripts.
Or, that the trusted site will necessarily know that what they thought was a "harmless" ad sever hasn't decided to do something more sinister.

Obviously, one solution is just don't check that option (or in Torbrowser's case, uncheck it).
However, in cases where other applications use NoScript & check this option by default, I wonder if most users even understand it?

[Giorgio Maone]

Tor Browser's case is quite different: since your whitelist can be used to fingerprint and identify you, by checking whether a list of popular websites is allowed to run scripts or not, and Tor's primary use case is anonymity rather than security, they explicitly funded the development of this feature and they're enabling it by default in order to prevent websites where you choose to run scripts to deanonymize you by guessing your whitelist (from the parent website standpoint, all the internet is whitelisted).