Price tags should be placed on all items. Once you get to the register and you have 15 items at the register, there are times when the clerk is unable to find the price of one item in the computer. As a person who has experienced this situation a number of times, I can tell you it is very annoying.
No. Shelf tags are enough. Add self scanners in aisles for folks to check prices if they wish to. Employees can be better used to actually provide customer service. I've also met numerous employees who battle repetitive motion injuries and pain from the pricing process.
It's redundant. The price is on the shelf, in much larger numbers, and with per lb., qt, count, etc. Stop marking every item and pass the savings to the customer.