Supposing you want to use web based testing with Droidium.
In such case, you have a pretty specific configuration in arquillian.xml, as you need to enable multiple containers.
However, if you don't want to run Android - you are for instance testing with Firefox, so no Android container is needed, then you need to create a separate <group> in order to do that.
Otherwise, MultipleContainer Extension will let Arquillian create container def for each <container> in the group, leading to attempt to create JBoss AS - or whatever is you web container - using Android container configuration.
This will obvisously fail, for instance with
So, if you put only multicontainer extension jar into <dependencies>, behavior is broken. If you don't put anything there, you already have tailed arq.xml to be used with multiple container. If you indeed put Android container there, it is started even if it would actually never be used due to fact you asked for Firefox Browser.
This represents a serious usability issues, hence marked as Critical.