Apps always felt too much ceremony for me too so a couple of years ago we went to one app by default and never regretted about that. This is a great article on that topic and it has other useful practices too.
Basically from my experience it’s not clear how apps helps until you want to reuse code between projects. You can easily avoid namespace conflict with some extra levels eg. static/<module>/image.jpg or template/<module>/template.html. To make apps loosely coupled you need to make an extra effort and plan beforehand and this is very hard to accomplish in agile world. I often even don’t know in what module should I place my model and it’s quite hard to move models between apps. In one app setup I don’t fear to make mistake by placing model in wrong module because it takes a couple of minutes to move it into another one when things got clear (and you know the fear of refactoring is the worst thing).
When I see that some module is really can be reused between projects or it feels like it better to be separated from the rest of the project to prevent developers to place project specific logic into it then it can be moved into separate app quite easily because it’s already loosely coupled with the rest of the application that’s why we are moving it from the main app. Even if it contains some project specific entities they can be quickly refactored out of it.
If you’re going to try one app setup then one thing that I would recommend is to get rid of app prefix in table’s names, follow article’s advise and always set db_table explicitly, with that change writing and reading sql become a lot better. In future you may use a checker that warns developers if they added model without db_table so naming tables won’t require extra mental energy.
Overall apps is a useful concept but I would recommend everyone to give a try one app setup and see if you move faster with it and do you face any problems that wouldn’t be possible in multi app setup. Would be good if Django docs had some high level overview of both setups so people knew that app separation is not required thing in Django.
UPDATE:
One thing I want to clear up is that we still use apps like module structure, so if we have one app named mystore inside it we place modules like this:
mystore/
models.py
users/
models.py
views.py
products/
models.py
views.py
this way we have many good properties that @andrewgodwin said apps have, eg. easy to remove some feature if it become obsolete and separation of concern.