The title of this post is one of the options when importing a CSV file. This may sound like an idiotic question, but it needs to be asked…
Does this pertain to ALL products in the store or just the existing data that's associated with each product that's getting imported.
If it's the former, it seems like the most dangerous check box imaginable (and I would assume it's just there for people new to the cart who want to delete everything in the demo store before starting to add their own stuff).
If it's the latter, I had assumed that everything would get overwritten when the new data gets imported as a matter of course (though I could well be wrong).
I can't exactly “experiment” with this setting for obvious reasons, so I thought I'd ask it here.
From what I remember it's the Armageddon one, for when people want to upload all items.
I thought it was the other way round Im sure I did it once, best option, just import 1 product with a slight change …go on I dare you 
That's what I would have hoped as well. Might be a poor Russian/English translation going on. Otherwise it's kinda like the “nuclear button” sitting there on Obama's desk. Sure, he probably won't press it accidentally while reaching for his coffee, but why would it be there in the first place???
Maybe someone here that has a demo store up and running will give it a go and see?
I just tested it out for you…
I exported 3 products.
Removed one from the import file and changed the product code and name on the other two products.
Checked the “Armageddon” button. Imported…
The original 3 products still exist with no evident changes. There's now 2 new products, as per the product code change.
I wonder if it means the 'Files' specified on the Edit Product > Files tab, only one way to find out…
Update: Yep, that's exactly what it does. It only deletes the 'files' from the product Files tab but only IF there is 'Files' specified in the import file. It won't let you import if you check this button and do not have products Files specified in the import file.
This reminded me, in Ultimate, it's a right PITA that product exports don't export the 'Store' column, never mind a value, just nothing. So to export then import the same file requires manual intervention to create a Store column and the appropriate “Store Name” values. Would put it on the User Voice but…what's the point?!
yes I was just browsing this too
Thanks for the insights guys!
I had posted this comment this morning on the “report a bug” board:
http://forum.cs-cart.com/tracker/issue-3764-imported-features-are-getting-added-to-not-replacing-the-original/
After I did, I got to wondering if the purpose of the nuclear button was to clear out any features that might have existed before the import occurred. Based on your findings, that's not its function, so I guess my bug find was genuine.
Import is rubbish, apart from anything else if you are importing products with all options, images etc it's so slow that it hits the server timeout and tonight I'm down to importing products 25 at a time. It should import the bloody data to the database and the workout creating images once that's down or step though it breaking on each product so it dosn't hit the timeout set on the server.