By providing your team with the same vagrant environment (usually as simple as committing your Vagrantfile to your repository), then you know everyone is working from the same page and whatever you are building is pretty much portable from one development machine to another.
If you have one dev running MAMP, another running from the default Apple (or Ubuntu/Linux) environment, another running something else, there is no consistency.
We have our vagrant in git and every developer has the same environment. We run on Vbox under Mac OS X. It has been a big time saver and is reliable relative to hosting the dev env natively on mac os x. LAOP stack with the PHP being provided via Zend Server. We connect to a enterprise test instance of oracle.
We are starting to build simple docker containers for python via RHEL SCL version and will have other docker containers to "play" with for a while. Maybe someday we will get rid of Vagrant. Not likely anytime soon.
If you have one dev running MAMP, another running from the default Apple (or Ubuntu/Linux) environment, another running something else, there is no consistency.