In Adobe Acrobat, what is the difference between Save As > "Reduce Size PDF" vs Save As > "Optimized PDF"

In Acrobat there are two options that appear to make files smaller;
Save As > "Reduce Size PDF"
and
Save As > "Optimized PDF"

In my tests the latter results in smaller files; which makes sense given it's name.

It's hard to track down exactly why they're different.
What do these options actually do?

1 Answer

Adobe's help on optimized pdf and reduce size pdf for acrobat XI

Reduce size

• resamples and recompresses images
• Removes embedded Base-14 fonts

Optimize

• Optimizer lets you set options for color, grayscale, and monochrome image compression, and image downsampling
• You can also make compatible with to ensure certain items don't get compressed that would reduce compatibility
• It also gives you control of other options not given in reduce size