Disadvantages of using multiple apps django
Divide et impera.
This is one of the basic rule of programming.
Divide your problem in smaller pieces and on the long run you will be happy:

Code re-usability
Maintenance
Elegance? 

Also if you are working on an opensource project your main goal would be to find someone else who is interested in it and that could help you. It is easier to find someone interested in something really specific than to find someone who wants to adopt your super-huge app which does a lot of beautiful things that nobody else like.
In django,What is the difference between creating multiple applications and using the same application and using all models and views in the same application? Will the latter create any problems?