Because it saves time. Let's say if you are a jquery # XX version and want to install jQuery # YX version, all you have to do is:
bower install jquery#YX
and then you can remove the obsolete version of jquery with:
bower uninstall jquery#XX
and also allows you to clearly define the dependencies in the bower.json file.
It also makes it easier to find documentation and the exact version of the dependency your project requires. Usually in the traditional way, you will either forget the version or the source from which you downloaded the file.
nkh
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