When you withdraw from your RRSP (before retirement), it doesn't reduce the contributions that you make during the year or in previous years. It reduces your lifetime contribution room. If you take out $5000 from your TFSA, then you can contribute that $5000 back the next year, so your lifetime contribution room will end up the same. But if you take out $5000 from your RRSP, then you will never be able to put that money back in.
