Breadcrumbs is a term used to describe a click path to the page you are viewing. It is generated as a line of links, usually at the top of the page so for example you might see
myalbum photos concert artists
Each underlined word above represents a level of category or sub-category, which you can click and jump back to.
The advantage is that you can see exactly the path of any existing page, relative to any upper levels that are nesting it.
In xoops software, this useful feature is often incorportaed into module navigation structure and shows up in the pages viewed, sometimes as links, or alternatively icons.
It is not currently used in the core.
Breadcrumbs are useful, and as far as I can see have no disadvantages at all.