For some corporate buyers G7 certification is important - even if they don't understand what that means. The majority of print buyers would be clueless.
The important thing is that you, as a print supplier, have at least one appropriate print standard, with supporting specifications, that you can reliably adhere to and that your proofing is aligned to it.
It really depends. What G7 is -- and all it is -- is a calibration procedure. Initially, it was developed for offset lithography, because it had been a bedevilment in that industry prior to computer-to-plate that there was no way to anticipate neutral tone curves on analog-generated plates. So each individual printer had pretty much their own closed-loop color system.
However with the arrival of computer-to-plate, it became possible to control neutral tone curves on plates, and in essence, that's what G7 attempts to do.
But that's all it does. End of story. Nothing else.
The idea became that since in lithography everything had become all about standards, and since there were standards for media white points, chroma values for ink, and densities for ink, that if you could determine tone value calibrations for a given set of standard parameters, then you'd need no individual ICC profile for that condition; a stock ICC profile built with those calibration values as its expected tone curves would work in all cases in that standard condition; i.e., Gracol or SWOP profiles.
And again, that's it. There's no more that G7 does.
So if that's what you're doing, then yeah, it has some benefit.
But if that's not what you're doing, it has none at all.
The important thing to remember is that unless you have standard conditions, then whether your calibration is some RIP-standard calibration routine or G7, that calibration is only a calibration; it's just a part of the machine state you must characterize with an ICC profile.
And it's the profile that carries the load. Not G7.
On a sidebar, a benefit of going through the G7 experience is that many printers are exposed to the idea of process control in print production. Assuming that the G7 expert is knowledgeable and educates the printer appropriately.