Illustrator question

I’m new to illustrator and I have a question about it’s main use…I mean, I know it’s a vector based program commonly used for making logos, etc, so they can be scaled to any size without distorting, etc…but…my question is regarding the intergration of pixel based images within vector layouts in illustrator. is this done often? like if I was to design something in illustrator and it had a photo or rasterized image from photoshop in its layout…what’s the point in designing it in illustrator?

thanx in advance

Fitz