I'm not sure I understand exactly what you mean regarding holding in a relaxed way. Would you be willing to explain a bit more?
My understanding is that relaxed grips like that of a baby, for example, are ideal because they allow for greater diversity of pathways for the intent to manifest through. I would agree simply standing there holding onto someone without any further intent isn't very good...if anything, it seems to invite a strike to the grabbing hand so nage has less dead weight attached to the arm/wrist.
A parked anything poses little danger unless it somehow has greater inertia and you smack into it. And once you've smacked into it, better hope it doen't start rolling on top of you or, still connected, move you somewhere you don't want to go.
I look forward to the day that a real attacker on the street will hold you in a relaxed way. That method may apply in the dojo to assist you with practice, but I have never seen or heard of this happening on the street, or in real life. Good luck to you.