FIXHEAD is used to reset or fix FITS headers with various pathologies.
ORIGIN and the related RORIGIN and CORIGIN cards are used to reset the FITS coordinate system cards (CRVALn, CTYPEn, CRPIXn, CDELTn, and CNPIXn). This is useful if the coordinate cards have been altered by programs (like IRAF or STSDAS) in ways that cause problems with various VISTA image manipulation programs, especially SHIFT. FIXHEAD ORIGIN can also be used to strip out wavelength calibration information (but you cannot uncalibrate a spectrum if it has been, for example, resampled onto a linear wavelength scale). ORIGIN resets the coordinate info along both axes, CORIGIN and RORIGIN only reset coordinates along the Columns and Rows axis, respectively.
BLANK is used to remove any empty (blank) header cards. While blank cards are allowed under the standard FITS definition for headers, they can be a nuisance as they eat up available header memory.
GROUP removes various header cards related to the ``group'' structure of complex FITS files. Since the current version of VISTA does not recognize the group structure, these cards are eating up header memory.
WFPC is used to remove header cards in WF/PC1 imaging data. Again, the
purpose is to try to free up header memory, especially in old WF/PC1 image
which have huge image headers.