The learning curve is much steeper with a dense interface. So if you only use a software occasionally you may be better off with a friendly looking interface that hides stuff from you unless you need it.
You make a really good point. Checking into a flight should not be buried into some dense corner of the website. Users need to do that in one click and not very often. A retail POS UI that's used daily should be optimized for dense logical layout at the expense of learning curve.
