[Poster is the CEO of an external illuminator company.]
There are a lot of benefits to using a separate infrared. Sadly, the industry has dictated that poor quality video is "good enough".
Education is key to understanding the differences between a camera with integrated infrared and an external infrared.
Why is the security industry the only industry that accepts poor quality video as video that is "good enough"? Poor quality video/photos are not acceptable to professional photographers, the broadcast industry, and even photos and videos for our own personal use when taking family photos, selfies, etc.
Separate infrared also helps increase bandwidth, keeps bugs away and spiders from building webs on the lens of the camera. The external LED illuminator also has a longer life span, offers longer distances (more true to spec) and more flexible fields of view to match the field of view of the lens on the camera to eliminate hot spots.
If you need something short range, cameras with built in infrared is an acceptable choice. For your more professional, outdoor, and high end applications where your client is serious about security and actually want to identify perpetrators, do yourself, and your client, a favor and offer a separate LED illuminator for best performance.
Iluminar offers a free 30 minute WebEx on the how's and why's of CCTV lighting.