Dude, you could prolly start a fire across the room with that thing!
And i bet the flash back from something that powerful could do YOU some damage at the worst possable time!
White walls, glass, mirrors and other reflective thingies, that all leads to bad things happening!
I have an OLight Javelot that is about 1200 lumens.
I also have an OLight Baton that is about 1000 lumens.
One I carry in the coin pocket of my jeans, the other has a lens that is wider than the Baton is long.
The size of the reflector and lens are important - even though they are similar in lumen rating, the Javelot illuminates a LOT more area because of the size of the reflector/lens - bigger is better all else being equal. For what it is meant for, it is quite sufficient - I put a diffusor over the lens to make it more useful; I really don't need to see something at 1km away at night, although it is nice to know it can reach that distance, there isn't anywhere around my house that is open that far away.
The other thing I look for in a flashlight, is how long it will last on its lowest setting.
The Baton will last 190 to 360 hours (depending on which Baton you have and whether you believe their ratings) at 0.5 lumens, which is enough to read by or see in front of your face - it is enough to navigate around the inside of a house, but outside I bump it up to 12 lumens to walk around and so I don't bump into a cougar or bear. This is my EDC. If I have to hoof it home, I would clip it to my ball cap bill and use it that way for a navigation and task light. I am sure it would last several weeks that way even if I use it every night, all night.
My Baton has a 'turbo' mode that only lasts about 30 seconds before it gets too hot and then it drops down to 300 lumens which is still plenty bright.
The Javelot will last 360 hours at 3 lumens which is the lowest it will go. That is more than enough to navigate outside with the diffusor which will illuminate a wide area to about 10 yards enough to identify objects. Without the diffusor on it becomes a spotlight that can identify objects to 100 meters or so. Bump it up to 1200 lumens and it is almost like daylight with the diffusor (except for shadows) and the rating of 1km is probably correct although I have not tested it that far. The next step down, 600 lumens is not that much different and just as useful for 99.9% of usage IMO, and the battery lasts a bit longer (almost 3 hours). At 80 lumens, the battery will last 12 hours and the illumination is plenty useful - and the spot without the diffusor would probably blind someone.
So, how much is enough?
It depends on the light itself and what you are using it for - a good sized flashlight like the Javelot, 1k lumens is plenty IMO, especially if you got a diffusor for it. I can't imagine anything I would use it for where I would need more than that.
With a small pocket light like the Baton, again, about 1k lumens is plenty - and at that size the flashlight will get too hot to hold onto. If you need more light, you are going to need to go larger, not necessarily more lumens. I am guessing anything over 2k lumens is just overkill unless you have very special needs - like a backup landing light on a jumbo jet, or a backup for a lighthouse.