It has nothing to do with accuracy... Today I believe the majority of conversions where part of the Sako extraction system is installed is for the money... and why install only part of the extractor system?.. leaving out the part that makes it safe if you ever blow a case.
Those who first altered the 700 extractor system did it to accommodate the 6mm PPC case. In their laziness only installed part of the Sako extractor system... and it was no problem until there was a case failure... then all hell broke loose. There have been at least one death and several injuries with Sako extractors blowing out on severe case failure. This is very old news in the Benchrest world.
I think the vast majority of those who do the conversion today do it for the money and could care less about weakening the 700 design.
Handloaders should be extremely careful when using a 700 with the Sako extractor... professionally I will not do that conversion and personally I wouldn't own one...
Here is how the Sako extractor system works in a Sako... with the 'bolt guide' actually working as a deflector when a case blows up... a feature those converting 700's do not install.