There are some impressive advantages to an online system, like CoManage, compared to a local program that needs to be installed:
It's often much less expensive than a classical system
It doesn't require any installation on your device
It works via your browser, thus usable on any device: Windows, Mac OS X, Linux, tablets, smartphones,...
It can be accessed anywhere there's an internet connection
Data is backed up daily, meaning data safety, without any extra costs
It's always up-to-date