You have to look at three things: total coverage limits, your deductible and "high value items."
Let's say you have less than the $1,500 limit in jewelry and your jewelry goes missing. If you have a $500 deductible, then the insurance won't pay anything, because it's lower than the $500 deductible. At that point, you would not even file a claim,
Now let's say your $6,000 watch is stolen. You policy will pay whatever the standard limit for jewelry is, again $1,500. Since the watch's value is more than the deductible plus the jewelry limit, you get the whole $1,500. Of course, you have a loss value of an additional $4,500 which isn't covered.
That's where the high value item rider comes in. For example, I looked at all of my limits of coverage, and for computers, jewelry, and firearms, the limits were completely inadequate to replace it all if a fire or theft took them. So, I pay an additional amount each year for a high value item policy rider. It supplements the standard policy limits for these expensive things.
Even if your total policy limit for contents is really high, you still need to verify these high value item limits. Normally the insurance company won't cover more than the standard limit for these things if the limits exist in your policy.
Bottom line: pretty much everyone has high value items that will exceed the standard policy limits. It's better to add that rider just to make sure!