The best explanation for it is found on page 8 of the manual. I believe it is only available for VI PRO 2 and not the free players. So look in your user area for the VI PRO 2 manual, and look at page 8. It's perfectly outlined right there. This is another of the many advantages of VI PRO 2. Humanization is only 1, of many. I believe VSL let's everyone read the manual, even if you don't own it so it would be a good read for those who want to know what it can do that your free player isn't doing.
I for one love the humanize feature and it's adjustable parameters (you can adjust what percentage you want of the script). Additionally, they have tons of presets that actually completely change the tuning and humanization. I no longer have to do anything with that to get what I want.
Time Stretching the samples, to make basically any sample become exactly the length I need it to play. A 2 second crescendo is now 3 seconds with a few clicks of a button.
Auto-Divisi. I can easily stack multiple samples and sections and have them split for me automatically. Is a nice feature.
Total number of cells is increased - I can layer a lot more samples into one icon because the total number of allowable cells per instance is increased. I can now put 8 instruments into one instance and pan them etc and or layer them perfectly in a snap. Instead of the maximum of 2 in the free player I think it is.
APP Sequencer - In long repetitive sections this works amazing for writing a long heartbeat styled base line or pizzicato section as well as any other type of sequence you want to create.
I am beginning to re-write the manual here so you would be better to go read the manual. The first few pages of the manual are specifically outlined with what's new etc. Page 8 will explain your preload buffer size.
**edit - another one I could never live without is cell disable feature and the presets made for VI PRO 2. This means I can load every sample of the entire instrument library ready to go, only all cells disabled (so no memory usage). All I do is double click the one I need and it loads that sample for me. No spending hours searching for samples etc. They are all right in front of my face.**
Hope that helps and no I do not get any favor points, free instruments or money if you buy VI PRO 2 because of this :). I have never even met anyone from VSL let alone work for them :).
Maestro2be