Tx is a tiled and mipmapped texture format, which will dramatically improve time to the first pixel, overall render time, and memory usage. Therefore converting textures to Tx files is highly recommended.

You can choose your preferred workflow of generating Tx textures:

• none: No Tx files are generated, the original textures are used. Note that this mode is recommended is special cases only because it can hurt performance.
• manual: Use the Tx Manager to generate Tx files manually when needed (e.g.original texture has been modified, color space has been changed, etc.). Existing Tx files are used in the render instead of the original images.
• auto: Textures are automatically converted to Tx files before rendering the scene. Textures are converted from the image color space to the render color space. Each 8-bit texture is converted to 16-bit float data type images to avoid quantization errors in dark tones. 
  This are the options passed to the maketx tool:

-u --unpremult --oiio (--colorconvert [image_space] [render_space] --colorconfig [config]) (--format exr -d half --compression dwaa)