There are many innovative and useful photography apps for smartphones and tablet computers. They will either assist the photographer with taking and developing a photograph taken with the device itself, or serve as an adjunct to the photographer.
My venerable first generation iPad is stuck with an outdated operating system and is therefore not compatible with many new apps. Nonetheless, I find it invaluable to my portrait photography. I use it to store, organize and display inspirational images that others have taken.
I often wander around in sites such as Model Mayhem. If I see a photo that has some aspect that I like, I save a copy on my computer. They are then organized into folders that are synchronized with the built-in Photos app on the iPad. My folders are organized primarily by what the model is wearing: Dress, Casual, Swimwear, Lingerie and Implied. Another category is Concept, consisting primarily of heavily retouched fantasy portraits. Cars is another, where models pose with a car or motorcycle. Headshot is another.
Further, I often split each category into two folders: one for vertical images and another for horizontal images. This eliminates the necessity of having to turn the iPad 90° to see the largest version of the image.
I have concrete steps in front of my home, and my wife has a Steinway piano. Both are great places for photograph models. I have a folder of images for each of these special situations: models posing on steps and models posing with a piano.
There are three primary uses for these images. One, of course, is inspiration: a nudge to get my creative juices flowing. The model can be shown an image to get some kind of idea of the goal in mind.
The second primary use is to give new models a posing guide. There are apps for this, but photos of actual models in various poses are easier to follow. Why is this? It is because a posing guide is just that: a posing guide. But what about the all-important facial expression that goes with each pose? This is where a nice photo on the tablet really comes in handy. Sometimes I will even place the iPad just out of the frame so the model can see it and come closer to nailing the pose and facial expression I am looking for.
A third use is to study the lighting in the photographs you admire. To this end, you could further develop folders such as Hi-Key Studio, Lo-Key Studio, Natural Light on Location, and so forth.
A high-end tablet is not needed. Most of the images for on the Web are low resolution anyway.