The primary advantage of voluntary deductible is the discount on premium.
No, no-claim bonus is a reward for not filing any claims in a given year.
No, co-pay is the division of total claim amount between insurer and policyholder.
The downside of voluntary deductible is the insured having to bear the majority of repair costs, thus defeating the main purpose of buying car insurance.
You should opt for a deductible only when you are positive that you can pay the sum as and when the need arises. Since the deductible can bring about a major cut in the your total premium price, you cannot refuse to pay the deductible once a claim is approved.
Voluntary deductibles should be avoided at all costs if you are sure you cannot readily produce the amount at the time of claims.
If you are sure that you are a responsible driver, opting for a voluntary deductible can be very beneficial. Since you are a safe driver already, you can rest assured knowing that you may not need to pay any deductible if there is no need to file a claim in the first place.