I think the point of plausible deniability applies to the notion that random data on your computer is circumstantial evidence that isn't particularly useful in getting a conviction.
They might not get a conviction for images of child sexual abuse, but they'll put you through the grinder to get you to reveal any encrypted data. The US has some protections and case law for this. The UK has RIPA and peoe have gone to prison for not revealing encrypted content. Some cases have maximum terms of 2 years but some have maximum of 5 years.
This needs to be factored into the risk assesssments of people using encrypted volumes.
