the marginal tax rate for RRSP withdrawals will be lower than the marginal tax rate when contributions are made

you are saving for emergencies

the marginal rate for RRSP withdrawals will be higher than the marginal rate for contributions

you are close to retirement age, and have little or no savings or pension.  RRSP/RRIF withdrawals may cause loss of Guaranteed Income Supplement (GIS) or other benefits.

further RRSP contributions will result in withdrawals which are high enough to cause a clawback of your Old Age Security.

when there is no RRSP contribution room available

for savings goals such as a vehicle, appliances, down payment for a house, etc.  The TFSA could be used instead of, or in combination with, the RRSP Home Buyer's Plan (HBP).

seniors who are not eligible, because of age, to contribute to an RRSP

young people just starting out, in a low tax bracket now, expecting to increase earnings and be in a higher tax bracket in a few years.  At that time, the TFSAs could  be transferred to an RRSP, making the contribution when the tax savings is greater.