I think its good stuff to have, just cuz your convertor have option to convert selected objects, that way you can check box show in viewport, especially if you don't have material in Mat. Editor so you can check if tiling is in order, it will save you one step, and as Juraj says its easy when you have few materials but if you have 20-30-40 or 100 it would make no sense to do it manually. Today when you have 3gb-6gb on graphic cards it wouldn't be problem at all, and if its optional i cant say how this can be bad thing, i know you have performance concern but machines today are more than able to handle that.
One example: Lets say i import chair or sofa or lamp... it is in Vray mats... soon i convert it to corona it will go gray, in order to see if everything is ok i will need to add that multi maps to ME and check show in viewport and that will be few minute job depending on complexity of object, if there is option in your converter it is easy just to check that option while converting and if UNC paths are ok it will be shown.
Well i wish you think about this once again, either way i think that this converter "rocks" :D