The folder is very important as it holds all the latest version of connectors (standard and custom connector) that you are using in the integration process. When you are running a process in test mode or deploying a process to the Boomi Atom, Boomi will download the connector binary file from the data centre and store it in the connector folder. This is how the content of the folder looks like in my Boomi Local Atom:
If you browse into one of the connectors folder (e, g. database), then you should see a zipped file (e.g, connector-database-35667-car.zip) which contains the necessary jar files for the connector.
Is that all? NO! 😀
Downloading the connector file into the connector/ folder is just part of the procedure. The next step that Boomi Atom will do is to extract the content of the zipped file to another folder call <boomi atom install dir>/work/connector. The concept is similar to how the Tomcat application server works whereby it will put all the working binaries into this folder and the JVM will load the binaries from here.
Sometimes, you will see that there are duplicated folders with a different version number.