Things to be aware of when using voronoi shaped traces
Here are some reasons that I came up with (as well as compiling reasons identified in the comments):

Your capacitance will be a bit more (especially if you have a ground plane on the other side). You can see a lot more coupling between two nodes that would normally not interact significantly. (David Tweed, Spehro Pefhany)

If you're migrating from a prototype board to a professionally fabbed board, you might miss any trace under-sizing issues in the design as all traces will be wider than drawn.

If you're migrating from a prototype to a fabbed board, your layout differences will reduce your confidence in the prototype testing. (Matt Young)

Drills can not be visually aligned (or visually verified) as it is not clear where in the shape the drill should have been.

Pad to pad isolation for SMT parts may be painful to enforce, and may cause problems in parts with thermal pads.

No ability to add thermal reliefs to pins (that I can tell).

Wider copper pours will make soldering more difficult. (Some Hardware Guy)

It obliterates text and annotations in copper layers.

Any separation intended for voltage isolation would cause issues unless a larger isolation bit was used. (Dave Tweed)
It probably depends on how big of a board you're making and how slow your milling machine is. If it's really slow, and a big board, then you could probably justify using Voroni shapes for prototyping. For a board that maybe takes 1-2 hours, I probably wouldn't bother with the risk.