Photography

uhhh, if it's inside the lens it will eventually cause image quality issues because it's going to get on the glass. Not sure how they know there is fungus inside the lens and it's not already on the glass

Could cause bloom and mushroom into a bigger problem.

I got a Tokina 28-80 f2.8 that ended up having fungus. It creates some nice diffusion funnily enough.

I'd be impressed such a new lens has developed fungus, what the heck were they doing with it

Be aware that a lot of what is called "fungus" is actually crystalline deposits from some liquid, probably lens cleaner, seeping between the elements. Fungus will cause permanent damage to lens coatings, but the crystals can be cleaned off without damage to the lens.

fungus inside lens tells me there's moisture inside the lens which tells me the lens wasn't taken care of and makes me highly doubtful that it "does not affect image quality". total pass for me.

It really depends on the lens, the position and the size of the fungus. I sometimes buy vintage with haze or fungus, and if I can I clean them up myself.

It doesn't really reduce the sharpness of the images, but causes a "glow" in bright conditions and around highlights especially at wider apertures; generally the impact is less severe than you would think.

I'd say a lens with mild fungus is worth something like half the price of one without, but this also varies with rarity and other factors.

If you end up getting it, you probably can keep it from growing further by UV sterilizing it (direct sunlight for some time) and then keeping it in a low humidity environment. As others have said, fungus can etch the lens coating, so some impact can remain even if you clean it/have it cleaned, nothing to be done about it.

Depends on how much you like tinkering with stuff AND with the specific lens.

In my experience most fungi in lens are either toward the front elements or towards the rear elements. Some lenses only require a few screws to undo the front and/or rear elements. If you are able to remove the affected elements, it is fairly easy to disinfect and remove the fungus, then wipe with a microfiber.

The elements toward the middle of a lens, generally speaking are harder to get to because you have to either disassemble the front or rear to get to them and also the zoom mechanism and autofocus motor tend to be toward the middle, so you have that to deal with as well if the fungus is toward the middle elements.

I once bought a canon 180mm macro for $400 because it had fungus. It was otherwise in excellent condition and it only took about 10 minutes to clean.

If you're up for it and the price is cheap enough, it can be surprisingly easy to strip a lens down and clean the fungus. Need a few special tools but not too expensive. Youtube is your friend!

First of all, if it's cheap enough (like 1/5th the normal used price) then sure, take it and do some tinkering with it. Second of all, how the hell did one of these modern lenses even get such a thing, i have only ever seen fungus/mold in vintage and relatively old glass like the first EF's.