The ease with which you can visualize all different types of networks, devices etc is very helpful for setting up new or maintaining old infrastructures.
I like that it's open source & free so there are no license costs involved! There isn't much i dislike about this tool but maybe if one wanted more features then perhaps their pricing model would have been better? We've used hava before when we were using older versions of Cisco switches/routers. This has allowed us to setup our routing tables easily without having to manually update them ourselves.