http://forum.xda-developers.com/showthread.php?t=2517430
It's far from perfect, and it's a known issue in Android that there's no such thing as unkillable. Launchers can redraw, Chrome windows can need to be reloaded, and LightFlow can be killed.
With that said LightFlow works most of the time, but the reason you need LightFlow is that the service sits there listening to notifications, intercepts the notification and then overwrites the system's LED settings.
By having the functionality built into the OS/framework, there's no 3rd party IFTTT-like app that needs to remain open. The OS has native vibrate and notification APIs. The LED notification is tied to it. Similarly, the OS has native autobrightness functionality already. An app like Lux intercepts the light sensor readings and then overwrites screen brightness outputs. The point in having native OS functionality is you don't need an app sitting there waiting, which is a waste of resources. It's a service that you risk getting killed because it's 3rd party. If it's baked into the OS, it's guaranteed to work.
And while Lightflow alone might not slow down your boot times, having Tasker, LightFlow, BBS, Lux all load up (not too uncommon for a tweaker) is noticeably slower than having CM boot on its own. It's also a far bigger resource drain. Consider the other services that must run in the background (3rd party SMS, Whatsapp, Timely, Google Voice, Google Search) and how some apps ALWAYS insist on running (Facebook, Google+, YouTube) even if you don't use them. There's plenty of apps that load on their own to slow down your system. Why add unnecessary startup apps.