In short, use the default settings: infinite.
If you use a short focus, like 1-2 meter, you will see bad far objects. From 5 to 100 meters, the differences are minimal.
Why? Because the two virtual cameras (left and right) are, more or less, parallel.
Don't use 0.5 mt! Everything is double! It's the same when you want to try your friend's glasses with 5 diopters! =)