Should I buy an individual disability insurance policy on top of my employer's?

Often yes, especially if you're a high earner, because group coverage has caps and weaknesses. Employer long-term disability typically replaces about 60% of income up to a monthly dollar limit, uses a weaker any-occupation definition after a couple of years, and disappears if you change jobs. The benefits are also taxable when the employer pays premiums. An individual policy you own is portable, can use the stronger own-occupation definition, locks in your rate while you're young and healthy, and pays tax-free since you fund it with after-tax dollars. The downside is cost — individual disability is genuinely expensive, often 1–3% of income annually. Buy it if your lifestyle depends on a salary that group coverage can't fully replace, and lock it in before any health issues arise. Get quotes while young; premiums rise sharply with age and medical history.