Reflection Lines is a useful Color Mode found within the Utility shader. It can be used to diagnose contour lines in a mesh when evaluating models.

This sort of shading is especially useful when modeling cars where surface evaluation is critical. Below is an example where it has identified some poor modeling in the hood of a car model.

Some more random examples below:

New to Arnold for 3ds Max? Below are some useful links to get you up to speed.

Changes to Rendering in 3ds Max 2018. More information can be found on the Area website (essential reading).

The MAXtoA user guide can be found here (if you spot any errors, please email docs@solidangle.com).

I recommend the Rendering Your First Scene page to get you started.

There are some tutorials here (more incoming in the future).

A basic material library can be found here.

The Learning Scenes are a good place for experimenting with rendering different features with Arnold.

The version of MAXtoA that ships with 3ds Max 2018 is already out of date. You can get the latest MAXtoA release here.

An introduction to Arnold 5 video for 3dsMax 2018 can be found below.

A 4-part (4 video) tutorial on the 3ds Max youtube learning channel on Arnold in MAXtoA:

More here.

Arnold 5.0 is now available. Please read the FAQ (MtoA) for details about transitioning to Arnold 5. More information here.

Some incredible work by Yuki Yoshida using Arnold for Maya. More examples on his website.

Zeno Pelgrims has created a nice dust shader for Arnold for Maya (MtoA).

Oliver Couston has created a great guide, showing the workflow from Substance Painter to Arnold.

I got some interesting results connecting texture maps to the UV Coords of an Ai Image shader recently.

A tutorial that shows the basic workflow can be found here.