Another benefit for me is reduced mistakes in picking items from the list.

Some people don't use online shopping because they worry pickers may make errors. My experience is that they do, but at a much lower rate than I do when I go myself. I frequently miss minor items off my list on the first circuit through the shop, and don't go back for it because it'd take too long to find. I am also influenced by in-store advertising, product arrangements, "special" offers and tiredness in to purchasing items that I would rather not. It's much easier to whip out a calculator to work out whether an offer really is better when you're sat calmly at your laptop than when you're exhausted towards the end of a long shopping trip.

You'd expect paid pickers to be better at it - they do it all their working hours, I only do it once or twice a month. Also, all the services I've used (in the UK) allow you to reject any mistaken items at your door for a full refund - which you can't do for your own mistakes. The errors pickers make are different to the ones I would, which makes them more salient - but they are no more inconvenient in impact on average.