From LightWiki

Working with the Rounder tool, found under Multiply/Extend in the default Modeler interface, you may come across some things you don't expect. The same can be said for the Edge Bevel tool. Both tools work completely as designed yet under certain circumstances they will not warn you that they are not performing correctly. Rounder has one warning message if you try and run it on points that have been unwelded or, a common mistake, on geometry that you have performed a boolean operation on and failed to merge points. Other than that, if will simply make hash of your object or crash with no warning.

With this in mind please take a look at these guidelines:

Rounder:

1. Always make sure your geometry is connected. After a Boolean operation, merge points before using Rounder.
2. Select the geometry you want to perform the operation on first. This is the best way to ensure predictable results.
3. Rounder will not work on open ends. The current (as of LightWave v9.2) tool is not meant to work that way. You can have open ends, just slice the edge so you have polys surrounding the operation and then delete them.

Otherwise the geometry that you select must be closed.

The basic function of Rounder is very straightforward. If you start getting into complex shapes then you have to open up the numeric requester and play with some settings. The numeric requester is really key here on more complex operations. It works in real time so you can play with it and see the results. This can mean the difference between something that looks like hash and a very predictable shape.

The only thing you have to remember is to use it with surrounding faces. Play with it, you'll soon see how functional it really is to make some nice geometry.

Edge Bevel:

The main thing to keep in mind about edge bevel is that the points you select cannot be on the edge of an open face. They have to be embedded in much the same way as Rounder. Consult the LightWave manual for examples.