Good advice …maybe it really is neglectable.
I did some further research, and what I read so far at least no information is ever getting lost. One just creates a new version of the attachment.
Max open calculation.xls
Moritz opens calculation.xls
Max adds "bread = 2 EUR" and saves the document
Moritz adds "milk = 1 EUR" and saves the document
The latest version will according to what I read include the row
milk, but not the row
However the second-last version will include the row
bread, but not the row
I could not test it yet, but if this is true at least no information gets lost.