Hi Berube, you're welcome!

Yes, Join is a type of "lower level" operation than booleans. Join on surfaces will only try to glue open edges to other open edges, while the booleans are more focused on intersecting objects with each other and removing some material. It can work to use Boolean Union similar to Join, but it can also cause complications sometimes because of its focus on intersecting the objects and dealing with the intersection curves and discarding material as part of the process.

The booleans are kind of like a batch-mode operation where they cut up objects where they push through each other, then discard pieces depending on where they were contained in which particular volume, then automatically rejoin the results. You can do the same work in a manual way using Trim + manually picking which pieces to delete + Join. These manual steps can be useful if you want to do some localized repair to an object, but for your regular workflow it can save time using booleans since they combine multiple steps together.

There are some more details on how to do this type of work in the object repair tutorial here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

- Michael