You would have to constantly hold the case to keep the potential difference 0. Touching the case that is not grounded will not dissipate static charge.
You are correct. It will however negate any potential difference which is required for two floating objects to zap each others. When you and your target float at the same +5kV potential for example there can be no discharge. ESD occurs only if you have, say, 5kV positive charge and your case (or object under it, connected to the case) has a negative charge. When you touch, sparks fly when your potentials are leveled (but not negated like when grounding). After your potentials are same no ESD happens anymore.
Same as when you get shocked by a sofa canvas. First touch zaps you, after that your potential difference is gone and you won't be zapped again unless you shuffle your vinyl pants enough to create static.
If what I say wouldn't be true, 99% of computer installations in this world would result in broken hardware since objects would just remain charged differently despite being touched. It would also mean that we would be all doomed to eternal static shocks whenever we move somewhere as charges would just remain forever.
If you think of it, what IS the ESD shock? It's a transfer of electrons from an object to another. When it gets strong enough it creates an arc. Now, once the electrons have been transfered via a medium (your hand) the system (you and the object you touch) have reached an equilibrium that negates further shocks.
I have one practical example for you: I have an electrostatic speaker. It's a sandwich structure with a 2 micron mylar sheet sandwiched between perforated steel plates.
The mylar holds a 4 kilovolt negative charge which keeps it flat centered between the metal stators at all times (well, except when you direct 1V - 7 kilovolts of AC to the stators at which time the membrane starts to move in pace of the AC, producing sound as it pushes air).
Now, the whole speaker is floating (it has to be due to design or it wouldn't be working in the first place). If I join the cables of the stators and the mylar membrane together, a spark occurs. Once. After that the mylar no longer remains centered between the stators because there are no electrostatic forces to keep it there anymore as the stators and the membrane have now reached the equilibrium. No further sparks appear no matter how I try to connect the + to the - or stator to the membrane.
Having said that - I agree with you Olds. It is always better to ground yourself by plugging your PSU and using the anti-static wrist wrap that is securely connected to a bare metal part of the case.
And see, now most of you learned something new - the working method of an electrostatic speaker lol. It's in essence a giant capacitor. In my case 6.5 foot tall and 2 feet wide. But only less than a half inch thick.
