InterMine uses Maven to manage local dependencies, for example your mine-specific data sources.
Previously, you had to download and compile InterMine. Now, instead, you'll be using the compiled InterMine JARs available via Maven Central. They will be automatically dowloaded and stored in the gradle cache ~/.gradle/caches/modules-2/files-2.1/org.intermine/.
To use your mine-specific bio sources, you will install Maven locally. The install task, recompiles the bio-source code, creates a new jar and installs it in you local Maven. These JARs are located in ~/.m2.
You don't need Maven if you don't have mine specific data sources.