Transferring Assets with Subledgers

We are on 9.0.  I refer to doc 786318.1, Question 5 which states that 'asset transfers involving subledgers, must be run at the end of the fiscal year and only after final depreciation processing has been completed.'

Can anyone explain why transferring assets with subledgers must be done at the end of the year as opposed to assets without subledgers which can be transferred at anytime?  What difference does the subledger make in this case that means it can only be transferred at the end of the year?  Is the transfer with subledgers only an issue if a certain depreciation method is in place, for example 'remaining life', or is there some other criteria which causes an issue to transfer assets non year end.  What issue does it cause and why?