The wires should be packed tight and tied with zip-ties so they do not interfere with the airflow of the case. The quality of the wire management depends on how much time you fiddle with it. If your case has a side window, you might want to make it extra good, so you don’t see cables in the case and you have a good, clear view of the motherboard.
Why do Wire Management?
First of all, the WM helps the airflow of your case, this in term, will keep your components cooler. With all your cables routed, there is less surface area for dust to collect on them, making your system cleaner, also, it facilitates cleaning the case or installing new components. You can easily take out your PSU if the cables are nicely routed, all you have to do is unplug them and get the PSU out for cleaning or replacing (keep in mind that if you replace your PSU and want to keep the old wires, you might have to get one from the same manufacturer, because not all have the same plugs) Your computer looks a lot better if there are no visible wires inside.
How to do a proper Wire Management?
As I said before, there is no science involved in making a wire management. All you need is some zip-ties and patience. It usually takes about 1-2 hours to completely route all the cables in the case, depending on how WM-friendly your case is. After doing some digging, I found a great video tutorial done by Linus, from NCIXTechTips, where you can see the entire process of making a good WM on a Corsair Graphite 600T case, which offers awesome WM capabilities. The process is the same regardless of what case you use, even for non-WM-friendly cases, you have the possibility to route the wires inside the case and still achieve great results.
Linus explains very well, but be extra careful and take notice of these tips:
Leave some slack in the cables, you don’t want the pins to come off. Keep them away from heat sources such as the video card exhaust or CPU heatpipes. Keep the cables away from fans, so they do not interfere with the airflow. Mount only the cables that you need, the fewer, the better. If you need to power other components in the future, you can add cables then.
As you can see from the video, the process is quite simple, but somewhat time consuming. I would recommend that you spend some time doing the wire management.