The new version allows focusing at different binning levels to what you're imaging at. Very cool.
This is great if you're imaging through narrowband emission filters and your current exposure value is too short to acquire a star to focus on. By binning you increase the chip sensitivity by combining pixels, thus allowing the process to find a star to focus on is easier - especially if the filter is extremely narrow i.e 3nm or 4nm bandpass. Once the star is found the HFD process can be executed. From my initial checks most of the other tweaks and bug fixes are "under the covers". I read somewhere that it now also supports Pinpoint5 for faster plate solves, but have not tested this.