Example using the Liquify Tool of Photoshop (Filter > Liquify...). This tool lets you alter the shape of sectors in an image.
In this example Liquify is used for changing a lineart drawing's shapes after being finished, since I realized later that various body shapes could look better.
I don't recommend to rely and use it every time like I did it here (I probably use it at some point in 2 of every 10 drawings) but instead force yourself to draw shapes correctly by hand. But there are situations when it would be faster to use Liquify as a quick fix than going back thru thousands of layers to correct some shapes.
As far as I know this tool is only in Photoshop. But on Krita, there is a Liquify brush tool that can be used in similar fashion on the fly.
Link to PSD file: https://www.dropbox.com/s/f3ivn4juj553820/Liquify%20Fix%20Lineart.psd?dl=0
Below: example of before and after and areas affected.
