Actually this "switch" does not do anything more than setting several OSM controls to positions that the manufacturer considers "optimal" for the next steps: SV calibration and color-critical work.
SV calibration can be done without switching to SV setting.
During the calibration appropriate controls are changed automatically.
North American 2490/2690/3090 models and SV calibration equipment can be bought separately. Assembled together, they create SpectraView monitor.

There has been a confusion about European 2690s.
According to many reports, Tag E SV switch is important for European models. The NEC 2690WUXI and the NEC 2690SpectraView are positioned as separate models there.
European "SpectraViews" are sold bundled with a different calibration software - SV Profiler.
Tag E switcher enables SV Profiler support. For a "regular" 2690 this option is blocked.
This restriction caused rumors that European 2690 are not hardware calibratable.
That's not correct.
Again, according to many documented cases, European 2690 can be calibrated with SpectraView II software. Same for the 3090.
We can expect the same situation when the NEC 2490 comes to Europe. What restrictions will be and how exactly they are implemented - we don't know so far.

The 2490 can be calibrated as a regular monitor too.
But in this case the benefits of hardware calibration are lost.