Originally Posted by gargamel

Regarding the OP's initial question, most relevant aspects have been mentioned. I just would like to add:

Package management with automated dependency resolution always relies on information that the respective package maintainer has added to his package, based on his very own, personal experience and quality assured in their own environment. If the package maintainer did a good job, the package management tool can make things comfortable. If the package maintainer overlooked something, that's relevant in your particular environment, it will either not work, add things you actually don't need to your system, or even screw up something in your system.