This isn't accurate.
No-clean fluxes are designed to not require cleaning after the soldering process because the residues are inert.
Bull shit. If this is the only criteria, then milspec rosin flux would also be no clean.
"No-clean" is a designation invented by manufacturers which is largely based on (or biased toward) esthetics.
Conductivity: In most cases, no clean flux residue is significantly more conductive and hygroscopic than a standard (say mil spec) rosin flux. And in many cases it is more difficult to clean, should you choose to. But it looks better. Most boards are machine assembled today with no cleans, and you can measure the conductivity of the surface of the board due to the residue. Between any two components that aren't even connected you can often measure conductivity in the Mohms. That is "normal." It's par for the course. But if you solder the same board with rosin flux, you won't measure conductivity, at all.
Corrosion:
fluxes are corrosive, those that are not "no-clean" can continue to to be active and munch their way through your copper traces.
Water based, perhaps. That's another category.
If you use too much of any flux, it will remain active for longer than necessary. Every single flux removes oxidized copper by eating it up with acid. (Elemental copper is unaffected, until it eventually oxidizes due to direct air exposure or through the oxygen dissolved in a solvent). Even no-clean flux has to be used in appropriate amount and with appropriate heating to dry it out. If your board is covered with sticky residue 5 minutes after you're done soldering, then it will remain active. But when you're finished soldering there is no exposed copper left on the board, anyway. All copper is covered with soldermask or tin. And the residue will eventually dry out on its own and after it dries and hardens, rosin flux is not corrosive or conductive and is waterproof. Whereas a water based flux will remain active as long as there is humidity and the acid doesn't all get neutralized. But you can just use less flux, if you are concerned. In automatic process/assembly, the amount of flux in the solder paste is predetermined, and the amount of paste on the pads is carefully controlled.
Go ahead and try to etch through a trace with rosin flux. LOL. Break out the heat gun. Expose to artificially high humidity and temps. Steam the board, maybe. Good luck.
If I'm not going to assemble a DIY board (no soldermask) for awhile, I sometimes wipe it over with rosin flux to clean and PROTECT it from air and humidity. Then it remains ready to populate and solder w/e.
Ever see the inside of a Zenith TV from the 70's. Globs of rosin flux residue. Those things would still be in service if they weren't obsolete. I know people who still have a B&W Zenith as their only TV in their expensive flat in Queens. (They don't watch much TV).
Now, if your goal is to have as little residue as possible, then you have to be way more careful when formulating and applying a flux. The majority of the bulk in a traditional flux residue is the rosin which is what ends up encapsulating the ionic residue (or any unused acid that may be added in addition to the rosin, which is an acid, itself, when it is dissolved in solvent) making it inert. When you try to minimize that protective residue for esthetic concerns, then you start playing games with trying to make the flux as weak as possible so the acid actually runs out and gets used up by the time the connection is good. If you are NOT concerned with esthetics/bulk of the residue, it is very easy to use "enough" and not have to worry about "too much." The only major side effect is the bulk/esthetics. It's not a problem of corrosion or conductivity.
But when a flux manufacturer tell you why you should use their "no clean," they will tell you all the 99% of the things it is formulated to do as if it is unique to their product (even though rosin flux does the same things with even better results regarding conductivity/corrosion) then add the esthetic superiority at the end as if that is just a cherry on top of other (ghost) benefits. It's great they their product still does all those other things pretty ok, but they have largely been compromised to some degree in the quest for esthetics.