Hi gmaasz,
This method is normally used when you are migrating assets into the D365, for example you purchase an asset with depreciation life of 5 years for 1000 euros, if you use straight line service you will depreciate 2000 every year.
Straight line remaining periods should be sue when you create an asset that is having depreciation life of 5 years but you already depreciate 1 year, so you will have:
Acquisition value of 1000
Depreciation of 2000
Net book value of 8000
You create the asset with a depreciation life of 5 years (60 periods if you use monthly depreciation)
Remaining periods of 48 so system will calculate 8000/48 = 166.66 if you multiply by 12 the result is 2000
Basically it is the same thing, but figures can change if we have decimals, that is something you need to check during your testing.
Hope that helps
Regards
Mauricio