I'm assuming you are allowed to transfer the RRSP from your employer to your own broker. Not all plans allow this. The GRSP I participate through work prohibits transfer of the contribution and the match as long as the employee stays with the company.
If I was allowed to transfer my group RSP, I'd probably do it once every year depending on the transfer fees. The typical transfer fee is $125 to $150. Your personal broker might be willing to refund the transfer fee as long as you transfer an account of certain size: say $15,000.
Note that you may have to sell the fund within the Group RSP and transfer proceeds in cash as many GRSP funds are not the same as retail mutual funds.