There's the loss of immersion / the way they might pronounce stuff not matching what you as the player feel emotionally but the main thing is you have to record every sentence for every single dialog in the game. From the big bad buy to the random NPC with a two-sentences exchange. If you don't the lack of voice acting compared to the other dialogues will be felt. This costs a lot, and can even result in decreasing the variety of the PC's dialog.
Also anyone wanting to make complex mods will either have to have a new voice for the PC for their mod; or have them be silent, which will again be jarring.
There's the loss of immersion / the way they might pronounce stuff not matching what you as the player feel emotionally but the main thing is you have to record every sentence for every single dialog in the game. From the big bad buy to the random NPC with a two-sentences exchange. If you don't the lack of voice acting compared to the other dialogues will be felt. This costs a lot, and can even result in decreasing the variety of the PC's dialog.
Also anyone wanting to make complex mods will either have to have a new voice for the PC for their mod; or have them be silent, which will again be jarring.