Update 2022:

I used the Photoshop Sketch app until it was discontinued in January 2022, then switched to Fresco. I resented it at first, but now thoroughly enjoy Fresco!

I make all of the art for the Daily Art Habit on a 12.9" iPad Pro with an Apple Pencil and the Adobe Photoshop Sketch app. I'm almost certain that I wouldn't have become an artist without these tools -- or at least it's a convenient excuse for why it took me so long! (See my previous post about being a late bloomer for that story...)

I absolutely love working digitally with this technology... here are some of the reasons why:

1. It's a portable studio with lots of brushes, almost unlimited colors and easy cleanup.
2. The "materials" are non-toxic. (I still distinctly remember talks given in my university art classes about the dangers of the chemicals we were about to use and the book Artist Beware.)
3. You have an eraser that can erase anything you want, even paint.
4. Made a mistake? Just undo it! (I can't count the times I haven't liked how my signature looked and redid it.)
5. You don't have to wait for the paint to dry.
6. Media can be mixed in ways that would be really difficult to do with physical materials... for example you can use watercolor over oil paint.
7. It's easy to incorporate photographs into your artwork.
8. No wasted materials!
9. You can paint or draw on different layers, reorder them, and change blend modes, allowing lots of ways to play and experiment.
10. Layers can be duplicated and transformed.
11. You can zoom in to do detailed work, and turn your canvas however it's most comfortable.
12. The program records all your strokes, which can be exported as a video.
13. You can rework your pieces AND keep the originals.
14. The artwork is instantly viewable in its native format. (It doesn't need to be photographed!)

 

You can also export your work to the desktop version of Photoshop and all your layers will be preserved. I think I would love Sketch even without this feature, which is why it didn't make it to the list above. 

Are there limitations? Sure. I regularly bump up against the 20 layer limit (at which point I need to decide which of the hidden layers I've saved are not likely to get used). When transforming layers, you can't skew them, only compress or stretch on one axis. I also find the incorporation of substrate textures into the brush tools can be a little annoying. For example, the rich oil brush will look like it's used on canvas, while the watercolor brush looks like it's on watercolor paper. 

Are there competitors? Of course. I know fans of both ProCreate and ArtStudio. I've decided to use Adobe Sketch until I feel I've reached its limits, and it's possible that may never happen.

Update 2022: As noted above, Adobe Photoshop Sketch app died in January 2022, and I switched to Fresco. For better or worse, it has a much higher layer limit... I've never hit it! It's possible to skew layers now, and to animate, and a lot more.