As you get older, your insurance premiums increase. This is due to the that fact that you become more likely to suffer from an illness or injury. This is the case under a stepped premium. When your policy renews each year, your premium is recalculated based on the risk associated with your current age. Whilst these stepped premiums are initially less expensive, the increase in risk each year, especially as you reach older ages, can result in premiums becoming significantly more expensive and potentially unaffordable.
Level premiums lock in your premium based on the risk associated with your age at the time you take out the policy. Under a level premium, the premium you pay will remain constant throughout the life of the policy and will only increase if the benefit increases if the insurance company increases its rates (which can effect stepped premiums too) and when the level premium expires and reverts to a stepped premium (usually age 65 or 70). In the long run, level premiums might offer significant cumulative savings in comparison to stepped premiums.