Though your HOA's insurance policy takes care of your building and common areas (like a lobby or pool), their coverage doesn't include your unit — its interior or your belongings (like appliances, electronics, etc.). Here are a couple instances in which it's good to have condo coverage.
Damage and theft protection
If a pipe bursts or you return home one night to find your condo's been burglarized, your HOA's master policy unfortunately doesn't cover repairs or the replacement of your valuables. Luckily, your condo policy helps pay for both.
Additional living expenses
If a fire or other unexpected accident temporarily renders your unit unlivable, who pays for your housing and meals in the meantime? Fortunately, condo insurance helps cover the repairs and your reasonable living expenses (like food and your hotel bill).