Many people have a difficult time deciding for how long a benefit period to buy.
Obviously, the longer the potential disability benefit, the more costly the disability insurance. If you are near 65 and have prepared financially for retirement, a short benefit period would be in order. If you are young and have not developed much net worth, a lifetime benefit should be strongly considered. The reason for this is simple. If you have a career ending disability in your 30s, the corresponding reduction in income would prevent you from building up your pension benefits, other assets, or even Social Security benefits.