>Also, since grand juries do not decide on guilt, there is no 5th amendment right to abstain from self incrimination.
IANAL, but I'm pretty sure that's not how the Fifth Amendment works. Wikipedia notes the Fifth Amendment right to remain silent is broad enough to apply even in civil proceedings, and mentions an example of it being used in grand jury testimony: https://en.wikipedia.org/wiki/Fifth_Amendment_to_the_United_...
Looks like I was wrong about self incrimination in a grand jury, but even given that caveat, a grand jury can be useful for breaking through the blue line. For example, a prosecutor can petition to grant immunity to a key witness, and if granted immunity, can compel them to testify about things that would normally be self-incriminating, in order to reveal testimony of criminal behavior of a partner.
IANAL, but I'm pretty sure that's not how the Fifth Amendment works. Wikipedia notes the Fifth Amendment right to remain silent is broad enough to apply even in civil proceedings, and mentions an example of it being used in grand jury testimony: https://en.wikipedia.org/wiki/Fifth_Amendment_to_the_United_...