Many of these processes are good, and some are even necessary. For example, some backup programs use them to make sure your scheduled backups run at the appropriate time(s). But I personally want to know when an app or an installer sets up a new background process. Partly because I like to know as much about what's going on with my Mac as possible, but also because as useful as the launchd system is, it can also be used for nefarious purposes: Someone with less-than-honorable intentions can use it to launch, or to keep running, malware or spyware.
How do you know when one of these background processes--in other words, a new launchd configuration file--is added? One solution is a clever utility called (ALOD for short), created by the Computer Incident Response Center Luxembourg (CIRCL). This utility monitors all the locations that launchd configuration files (and other types of background programs) are stored:
~/Library/LaunchAgents
/Library/LaunchAgents
/Library/LaunchDaemons