One of the reasons I still use paint tool sai

over artrage is its ability to easily color only inside a determined area,after that area is specified. And specifying that area can be done with three different tools that make it a precise and easy process- first of all selection is easy to spot by the human eye- its marked in blue color,instead by a feathered border (like photoshop)- that way its easy to spot an area that is not selected.

After I do the inking,I usually first select with the wand tool- it can select by color or transparency, on just working layer,or on all layers. It usually does not manage to mask everything in blue. Thats where the select and deselect brushes come in handy- they pick up pressure sensitivity- that makes them perfect for filling in small and bigger areas which are yet not masked.

After everything is masked, its easy to just fill it up with the bucket tool and then proceed with shading/light and coloring in that area in general,without having to worry about spilling paint outside of the borders. The final image is sharp and no detail is lost.
I can always come back to that layer and LOCK it,so it colors only inside that area again.

Whenever I paint in artrage,the final image usually comes out blurry.I lose a lot of lineart and detail. I have to always sharpen it sligtly in other software.

I know that its possible to achieve some of that functionarity in artrage,but it is nowhere near what sai does.