Financial institutions may charge an annual administration fee. These used to be tax deductible, but are no longer. Thus, if you pay the fee directly yourself, you will do so with after-tax dollars. Instead, the fee may be paid from within the RRSP/RRIF. Effectively, this amounts to a tax deduction, and is therefore preferable, because there will be fewer dollars in your RRSP/RRIF as a result to draw out and pay tax on.
The same rules and advice applies for investment counsel fees.
Brokerage costs for buying and selling securities and fees related to buying and holding mutual funds must be borne within the RRSP/RRIF.