DeskPRO already supports custom fields stored about your users. They work fine if you want to record information that can have the same range of values across all your users: their shoe size, or their birthday.
But what if you want a field that has different predefined values for each user?
Suppose you sell custom pet accessories, and you want to record which pet a ticket is about. The possible values for User A might be "Fido" and "Tigger", whereas those for User B could be "Shadow" and "Felix". A normal custom field won't work.
Now you can handle this sort of information with per-user custom fields. You can create a field that has different possible values for each user and edit them on the user profile.
When your users submit a ticket from the portal, they can select from their own, personalised values, or even update them.
And of course, we've added per-organization fields too. You could use them to record buildings in an organization, the server or domain a software problem relates to - whatever information you need to track with different values for each user organization you deal with.
Our admin manual has full details of how to use per-user and per-organization fields.