That method will format the on_change parameter that you receive from the x2many field of the form

the meaning of options 0,1,2,3,4,5,6 are found in openerp docs field methods

Example on xml: <field name="list_ids" onchange="onchange_list(list_ids, context)"/>

let say our one2many field is 'list_ids' and inside it we have the fields 'amount'(float) and 'analytic_account_id' (many2one)

when we create a line inside the list_ids variable will be like this:

[[0, False, {'analytic_account_id': 33, 'amount': 800}]]

after you format it with values = self.resolve_2many_commands(cr, uid, 'list_ids', list_ids, ['amount', 'analytic_account_id'], context) it will look like this:

[{'analytic_account_id': 33, 'amount': 800}]

but if you are editing a one2many field it will only bring, the field you are editing: if you only change the amount field, it will look like this

[[1, 201981, {'amount': 500}]]

but you will probably need the other fields, so you format it with resolve_2many_commands again, and get:

[{'analytic_account_id': (33, u'ANALYTIC ACCOUNT NAME'), 'amount': 500}]

now you have the many2one in the form of an object, it is different when you change the one2many in the form because then it will be show as an integer id.

this way is easier to construct your on_change_methods, because you will always get the fields you need, no matter if they where changed inside the form or not.