Position relative can be compared to the margin property. However, they do affect elements in different ways. Adding margin to a element will push other elements away. Position relative, though, will not effect other elements.
The way I like to think about it is that margin is pushing, while position relative is moving. In the example below, we have three sections containing two articles. Normally we don’t want these articles touching each other, so we want to add a bit of space between them. The first section is using margin and the last two are using position relative.
Take note of how the last two are not moving the section title or bottom article when being positioned and even going over/under them.