Gnome 3 introduced a very handy feature, grouping multiple application windows (whether they be separate instances or not) into a single desktop icon. This means when <alt+Tab>ing through your windows, you can skip over the dozen firefox windows, then dive into just your terminal windows. Generally, this works great, and I think most users don’t have any issues. However, some people (myself included) use a lot of terminals. Some are temporary short-lived generic terminals.