How do I know what requires DAC?

Playing around with SQL Server, I came across a [semi-cryptic error](https://dba.stackexchange.com/q/193333/2639) . Essentially, I only need to log into DAC. Is there any general advice for when DAC is needed? How do I know I need it to access sys.sysobjvalues without googling for the error message? What all does DAC provide access to?