The actual folding mechanism is simply wrong and unreliable.
I often work with big files and use folding to speed up my work.

But, if the file has a wrong indentation (something not rare if the files are human edited) atom also fold the code in a wrong manner.
This in some case can be extremely dangerous , because if you don't remember to check every time what is folded you take that as given and work on the other parts of the file in a wrong manner.

The actual code folding is based firstly on indentation then on grammar.

I think that the code folding should be based ONLY on grammar.
Because, actually, even when you have a correct grammar (with correct folding rules) you can't be sure that the editor fold the code in the right manner.

Here is some examples to show , editing an XML file (i want to fold at line number 10):

Unfolded text (with wrong indentation at line 18 and 19):

Folded text (WRONG because of wrong indentation):

What the correct folding should be:

But for achieve this we must fix the indentation (on line 18 and 19):

I think that correct indentation CAN'T be a requirement to correct code folding.