This photo-editing app is meant to solve photo issues such as -

1.) There are certain individuals in the background who did not give their consent to have their faces published; publishing the photo - even if the subject in the foreground is entirely someone or something else - would mean violating their right to privacy; 
2.) There are unsightly elements in certain areas - an overflowing trashcan, the toilet, litter; these would serve as distractions from the subject
3.) Sensitive material and private information could be accessed if the image is zoomed in, possibly risking someone's safety and privacy
4.) You want to give the illusion of an improved depth of field

It is possible to freely fiddle with the blur tool. As you select the area/s you want to edit, you have the option to increase its blurriness - which means the selected area is going to have less a distinguishable form/s or shape/s, and will hence seem more gaseous than solid; you also have the option to use the tool to a minimum degree.

It is possible to apply the blurred area in a particular form. If you are going to utilize the 'shape' feature - it simply means the blur is going to follow the direction of the shape of your choice - a rectangle,  a flower, etc.