Many times... I see people working on images trying to do intricate editing but they are zoomed out way too far. The results? Usually its things like very poor clipping paths, masking, or odd areas caused by lousy selections. In my eyes and many others, this is just considered lack of attention to detail and is really thought of as unprofessional.
My advice... if you are working on trying to mask an object or create a selection, touch up an area, etc., you should zoom in on the area you are working on so it nice and big. Yes, this means you might have to move the area around in the window but... that is why they made the space-bar turn into that handy grab tool in Photoshop and many other graphics programs. Usually, no matter what tool you have active... just pressing space-bar will bring up the hand icon allowing you to move the canvas area around the screen without moving the window.
Working this way will ensure that you are getting the tightest selections and best masks possible. Don't settle for "looks close enough" because many times... close enough is not what you thought on the finished product. So remember, ZOOM is your friend and will help you get the best results possible by showing you what you missed.