lol it has no weight it only sucks power its not an issue.
can you explain why I would want 3 AFMU on my Anaconda?
Well 2 is enough. However I had 3 during round trip. 1 was "main" to repair FSD only after NS boosted jumps and 2 others for the whole repairs in case of need. That what initial plan. Couple months later I just used it 1 by 1: this repair is done by 1st, then by 2nd, then by 3rd - to equally load balance. I felt like I spend less materials to reload AMFU
But yeh, now I fly with 2 only.
AMFU is a filler module. It has no weight. So if you have empty slots and have no idea what you need there - put AMFU.
2 AMFUs make life simple. I love to have 100% everywhere. So you do all 100% except PP. Then reboot/repair to fix power plant, then do all to 100% again, repeat until PP is 100% too (well, I think 95% it will stop, repairs work for less then 95%). And here you must have 2 AMFUs.
1% you say is just unacceptable for me
I will go crazy looking on it.
Reboot/repair takes integrity from other modules, often including the only one that cannot be repaired (power plant). Since power plant integrity is the ultimate limiting factor when it comes to a ship's endurance, cannibalizing it should be a last resort if one doesn't know when one will be able to dock next.
A second AFMU is very rarely needed and it's also possible to destroy all one's AFMUs, but there isn't much reason not to take another, if there is room on the ship.
Unless they changed this recently reboot repair doesn't repair modules that aren't broken and can only bring those up to 5%.
95%
above 95 is not possible, reboot just deactivated. It was always so since 2019 I play the game.95%
I am positive you're mistaken. Reboot can be initiated with no damage at all, but cannot repair modules that aren't broken. I just tried it.
Remember, AFMUs have no mass. So if you have slots you don't occupy otherwise, put an AFMU in it and power it off. There is no downside to carrying one (powered off) apart from it taking up a slot.
Prior to fleet carriers my long distance deep space lone wolf exploration ship carried 2 AFMU. Now I don't care about AFMU. I made regular use of DSSA carriers until I got my own. Also the introduction of cruise assist that automatically stops the ship after jumping... preventing from flying into the destination star.
If you are going to do lots of planetary landings have decent shields. You will eventually smack your ship. Especially if you think you are going to do any exobiology.
As mentioned on other posts I suggest you make use of DSSA fleet carriers. If for no other reason that a game-save location. It pretty much sucks to crash your ship after several months in deep space and respawn in the bubble with complete loss of your trip. Gone.
If you are going to do lots of planetary landings have decent shields. You will eventually smack your ship. Especially if you think you are going to do any exobiology.
As mentioned on other posts I suggest you make use of DSSA fleet carriers. If for no other reason that a game-save location. It pretty much sucks to crash your ship after several months in deep space and respawn in the bubble with complete loss of your trip. Gone.
It is my understanding that damage is shared across internal modules. An AFMU will take damage that other modules would otherwise take. So an AFMU is prefereable to an empty slot.
Another hint, feel free to disregard. When you are fully geared up for your big mega deep space trip.... just go on a 1 week trip first. Travel maybe 5-10 kLy and get the feel of your ship and the loadout. Land on some planets, bump your ship around a bit etc. You will likely find a few things to make it all better. Return to the bubble, do some fine-tuning... then bon voyage! 
I thought I read something ages ago about them working like passive heatsinks, so people were filling up empty slots with them. Not sure if there's any truth to it.
Having more than one increases the overall repair speed. But if you're repairing that often or can't stand the wait, maybe exploring isn't such a great career choice.
I thought it was more to do with the Power Plant integrity.
If you have an exploration ship with say 250 module integrity spread over 10 modules and you have an incident that will deduct either a fixed amount or a percentage, and you compare it with the same ship having 300 integrity over 15 modules, having the same incident... then the only non-repairable module, the power plant, is likely to be less affected when you have more to spread the damage over.
That makes a lot more sense.
Sorry... won't do that again