I also use them for “simple” projects. I have a set of Task TODO keywords for one-off tasks. I have a set of Project TODO keywords for projects. Typically a project is a heading with a Project keyword and a number of (level + 1) headings with Task keywords. For projects that span several days/weeks this works well. 

Some things that I do fall between Project and Task in the complexity. The items needs 1-2 things done and discrete and different points in time (temporal dependency, first A then B) or with different co workers (collaboration) or both. The overall work, however, will only take 0-2 days. It's too big for a single task. It's too small for a Project. It's related items that conceptually belong together. In Goldilocks fashion, a check-box list is just the right size.