A segregated fund is an investment fund that you hold within an insurance contract. The term "segregated" refers to the fact that your investment is separated from the general assets of the insurance company. Your insurance contract dictates the insurance protection you receive. So segregated funds are an insurance contract that provides you investment management plus protection.

a) Death benefit guarantee - on the death of the policy holder the company must pay out at least 75% of the original investment minus any withdrawals. Different levels of guarantee are marketed and a higher guarantee comes with a higher cost.
b) Maturity guarantee - ten years after the money is placed in the policy the policy holder is entitled to a value of at least 75% of the original investment minus any withdrawals. Again, different levels of guarantee are marketed and of course the higher guarantee comes with a higher cost.

The reset feature simply allows you to "reset" the guaranteed amount at the current market value and reset the clock on the time required for a guarantee. If an account started at $10,000 and increased to $13,000 over three years and was reset, then the policy holder must wait 10 more years for the guarantee of $13,000 to have effect.
As an example, Mackenzie has a segregated version of the Cundill Value Fund. For a 75% guarantee you pay 0.35% more per year and for a 100% guarantee you pay 0.75% more per year. Note that the guarantees only have value if you die or wait the full 10 years since the last reset.

If you invested $10,000 in the 100% guaranteed version of the seg fund and the regular fund earns 0% for 10 years then the seg fund version would only be worth $9,275. The insurance company would have to pay you $725 but the regular fund would already be worth $10,000.  Higher costs = higher probability of losses.

If you invested in the 75% guaranteed seg fund and the regular fund earns -2.5% average for 10 years it would be worth $7,763. The seg funds costs 0.35% more to operate so it would be worth $7,489. Since the seg fund guarantees 75% of $10,000 or $7,500 they pay you $11. In short, the 75% seg fund is only useful if the regular fund doe worse than -2.8% over 10 years.

If the regular fund earns 10% over ten years it would be worth $25,937. The 100% guarantee seg fund would earns 0.75% less and be worth $24,266. In other words you would have lost opportunity of about $1,700 by using the seg fund. For any positive return generated by the regular fund the seg fund will earn 0.75% lower returns.

I note that the possibility of a broadly diversified fund earning less than 0% for any 10 year period is very very small. I believe it does not make sense to pay an extra 0.75% each and every year to ensure you do not lose money over 10 years.

My conclusion: while there may be some benefit for creditor protection (not discussed here), seg fund guarantees are not worth the extra costs.