When you just want to draw, using pixels is more organic and nearer to the traditional painting. Photoshop is full of pixels and details of it on any image you create. A painting or drawing you do in photo shop is full of a number of pixels and the details are the number itself.
Drawing something to illustrate digitally is an artist’s creation. And when it comprises of various shapes to make the final picture, those shapes are called vectors. Adobe Illustrator is meant for vectors. It has a varied style and hence when an image is complete there is no loss of quality. A good quality image is obtained through vectors. There is no restriction of pixels when you are drawing using vectors and hence resizing it easy. It is best suited for designing graphic logos.
One of the most important terms in the field of digital illustration is the resolution of the picture or image. There is a set standard for every image uploaded to a software or e platform. If you are illustrating digitally for a particular e platform, it is important to know the set resolution for that particular portal and design accordingly. This is in concern to space issues and should be closely watched out. Also, when you know the resolution details prior to starting a design, you will be able to accommodate every detail needed in the image for illustration.