Depends on what gear you have. My impression is that now it's pretty much pointless to even have binocs or scopes for farming; except at the edges of the world, enemies spawn just outside where you can see.
From my testing, it doesn't make much difference, since they still despawn within a couple seconds once they are out of range of your gear. You can easily check this on the surface as soon as you get a radar. Lay out a "skybridge" 2-3 screens long just over the tops of the trees. Run a rope up 44 blocks. Climb to the top. Add ropes one by one until the slimes despawn. (Underground, at night, in the jungle, and during the rain you have flyers to confuse the issue.) Repeat the test with whatever gear.