Recs.
Updated
Specs
Pros
Pro Simplicity provides more flexibility
Bower doesn't try to handle too much of the workflow process, which means it's more flexible, and can be incorporated into more workflows. It tries to just do package management well and nothing else, which is why so many workflow wrappers support it. Because it doesn't try to do too much vertical integration, it also means that the list of supported components that it manages is huge.
Cons
Con Seems like a redundant package manger
NPM with Webpack/Browserify can handle all the dependencies for both back-end and front-end. The only place where Bower may be useful is for projects which use libraries not supported by NPM, such as Polymer.
Con Does not store components in a registry
Bower installs components directly from urls and repositories, which makes it more susceptible to components being taken down, with fewer guarantees about their availability.
Con Difficult to create bundles
To create a minified bundle of all the required JS dependencies other tools need to be used.
For example a JavaScript task runner which will automatically concatenate JavaScript files and minify them will be needed. Although it's done automatically, it's still extra work because the task runner needs to be configured.
Recommendations
Comments
Flagged Pros + Cons
Con No benefit for a front-end developer to use Bower over npm
All benefits provided by Bower are provided by npm as well. On top of that, npm includes additional functionality.