Other regular delays seem to come from staff being perplexed by the complexity of the checkout system.
Also, mostly middle aged women being taken by complete surprise they are being asked to pay for stuff which leads to much fumbling around looking for purses and wallets and then they'll insist on counting out the exact change.
Then the constant 'Do you need a bag?', 'Do you want a receipt?' 'Do you have a stupid loyalty card?' routine.
Bring on automation please and make the world a much more happier place!
Restocking is already a cost stores have to do. Restocking is also something which isn't too time sensitive - you can do more restocking at night if needed. It's also possible to design the shop to require less restocking, by for example having deeper shelving units where products slide towards the front.
Helping people use the app won't be needed as soon as it becomes universal.
The only remaining cost becomes store security, but if everyone has an attached account which has been verified by a passport, even security might no longer be needed. Just bill people for the items they take, ban them if they don't pay the bill, and call the police and ban anyone who is violent.