My understanding of the post is it would host learned models. You'd train them wherever, but host the learned model in algorithmia, which exposes it through an api, making it easy for others to use your model.
It takes big data to train but that trained model can work on "small data" or big data. One-off uses for apps really do lend themselves well to a hosted solution like this IMHO. If you need to classify lots of data – then you are probably at a point to either train your own model or buy it from the developer via this site, I'd think.
Because if I am capable of training a fancy pants deep learning model to do something helpgul, obviously I need a service to host my model so badly giving someone my model is a better idea than paying $10 a month for an EC2 instance.