Expense tab entries are direct posting to the Chart of accounts.
Think of Items as More Meaningful to your Business activities. The Items List describes what your business makes, does, sells, buys, or buys and sells. Items control the flow of the data to accounts. They can be used for P&L or Balance sheet or both. One Item can be linked to Two Account = Two Sided Item, to show this is something buy and charge back = expense and income for that same item. Now you also get Item Profit reporting. Items allow you to use Quantity, to track cost and/or price and even for that same one thing as Both.
Anything you will enter and Job Track = assign the customer name, I recommend using Items on the Items tab. The Job reports rely on the use of Items.
Open Help and search on "Work With Items."
Here are the video tutorials:
I have attached an example of a report showing "no item" at the bottom = we didn't identify what this is. Along with this, you can see other details that Make sense.