Few things are always good or always bad. It depends on context.
If the files in your directory are just static files that you want your users to be able to download, then turning on directory listing is fine. This is quite common for e.g. software distributions, where you might have different folders for different versions, operative systems, etc. Letting the user browse around in these is not harmful - it's probably the use case you built the site for.
On the other hand, if you are hosting something more complex like a dynamic web applicaiton, turning on directory listing is probably a bad idea. You risk exposing the programs internal structure or even worse all sorts of config or log files containing sensitive data. It's easy to accidentally leak your DB password this way.
Another aspect to take into consideration is that the directory listing will probably telegraph what webserver you are using, and maybe even what version. You may or may not care about this.
So, the bottom line is this: Make sure directory listing is off, unless you know what you are doing, you are only serving non sensitive static files, and you have a specific use case that needs it to be on.