I leave it on or select mode 2 for motorsports. Rather annoyingly Ive accidentally switched IS off several times without knowing it while handling my 70-200 IS. This happened quite often on the MkI version of this lens and I need to monitor this behavior on the MkII. If it occurs again I will probably tape a small piece of toothpick in the gap next to the switch to keep it on.
5D3, 5D2, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 24/2.8, 35/2, Ʃ35/1.4, 50/1.8, Ʃ50/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200/2.8L IS II, 1.4x II, 2.0x III, 70-300L, T28-300 Di VC PZD | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC CS, Metabones SB | Vintage FD & FL glass.