When should I use dipole correction?

I am trying to understand the function of dipole correction in DFT. I find that there are two examples related to this topic on the VASP wiki.
The first case is about CO on Ni 111 surface
The input INCAR file is :

 general:
ENMAX = 400
SYSTEM = CO adsorption on Ni(111)
ISMEAR = -5
ALGO= Fast

LDOS:
LORBIT = 11

workfunction:
IDIPOL=3
LDIPOL= .TRUE.
LVHAR = .TRUE.
#  LVTOT = .TRUE.


The input INCAR file is :

SYSTEM   = H2O_TiO2
ENMAX    = 400
ISMEAR   =  2
SIGMA = 0.05
EDIFF = 1e-6
EDIFFG = -0.05
IBRION = 2
POTIM = 0.5
NSW = 200


Apparently, the slabs of these two cases are both asymmetric, but it seems that the second case doesn't set dipole correction.
As far as I understand, when the slab model is asymmetric, I should always use dipole correction. My question is:
When should I use dipole correction?