section 154"rectification of errors"

1-Section 154 –“Rectification of errors “

Under this section whose mistakes can be rectified Assessee’s or Assessing Officer’s?

2-What are the consequences of an incomplete income tax return

e.g. if Depreciation is claimed but no detail is provided in return 

&  Advance tax is deducted in tax liability computation but no detail of challan no. ,bank etc is provided in return.