<Hierarchy> Sequence Order - This determines where an item is in the project hierarchy, I would not use this in a view.
<Work Item> Baseline Due Date Variance - This is the difference between the baselined due date and the current due date.
<Work Item> Earliest End Date *- This is just a date field, I don't think there is any system functionality tied to this.
*
<Work Item> Earliest Start Date - Same as above.
<Work Item> Impacted By - This shows the work items that are impacting the selected item (ex: a child task, when updating % completion for a child it will roll up and impact the selected item)
<Work Item> Impacting - This shows the work items that a selected item is impacting (ex: parent items, when % completion is updated, it will roll up to the parent).
<Work Item> Priority - A numerical field where you can put in any number you would like. 500 is the default value (same as MS Project), but you can use whatever methodology you would like.
<Work Item> Risks - These are risks that are impacting the selected work item.
<Work Item> SKU - There is no functionality associated with this field, it was designed to tie products back to the selected work item. Usage here (like many of the fields) is not required.
<Work Item> Task Type - This is a picklist field designed to be customized with your own values.