On this short but useful video, Photoshop expert Jesús Ramirez (from the Photoshop training channel) demonstrates a way to make better cut out in Photoshop and not miss any spots.
This might have happened to you. You were working on a mask just to realize later on that you missed some spots. If you noticed that and fixed the problem in time – it should be fine but if you discover that after you print or send the work to a client – that could be a much bigger issue.
If you want to avoid those issues Ramirez has a solution for you which is super simple and yet looks very effective.
In Photoshop go into the layer and click to open the layer style and click on stroke and choose outside, (opacity 100%) and increase the size (depending on your layer) and choose a color which will give you a good contrast.
Now zoom in and take a look at the layer mask – if you have pixels which do not belong choose the mask and using a black brush to remove them (with the right size brush).
As we said – simple but very effective and it only takes a few minutes which can save you a lot of embarrassment later on.