I think metering usually helps and often spreads out the incoming cars enough to where the merging has a better chance of happening. But sometimes those meters are pointless or make it worse.
On my way to work I enter at a meter so close to the highway that it is impossible to get up to speed in most vehicles before being forced to either try merging into traffic with a large speed disparity or be forced to stay in the lane and take the next exit so you can try again. What's stupid is the area behind the meter light has enough room for about 40 cars yet I've never sen more than 10 at the height of the rush. Most of the time it is 2 or 3 cars.
On the way home the on ramp is so popular that traffic does back up and plug up the right lane of the other road which ripples back through all of the other secondary roads and makes a real mess of things. However, the meter is far enough from the highway to allow getting up to speed in all but the slowest of vehicles despite it being an uphill climb to the highway. Unfortunately trucks use the ramp too and they can't climb the hill very quickly so what you get are a truck and 3 or 4 slow moving cars reaching the highway in a tight knot.
Both metering lights fail to be effective when traffic on the highway slows because the bottleneck becomes the merge point and not the metering light.
For anyone driving in Oregon here is ORS 811.285(1):
A person commits the offense of failure of a merging driver to yield the right of way if the person is operating a vehicle that is entering a freeway or other arterial highway where an acceleration or merging lane is provided for the operators use and the operator does not look out for and give right of way to vehicles on the freeway or other arterial highway.
Emphasis on "look out for" is my own. Obviously in bumper to bumper traffic the polite thing to do is merge with every other car even though the vehicle on the highway could legally block the merging cars from entering.
Similarly there is a law for what to do at yield signs and one that says you can't operate "in a manner that impedes or blocks the normal and reasonable movement of traffic". So I'd say if traffic is flowing smoothly at 55+MPH and you jam on your brakes to let a car merge in then you've broken Oregon law. Not that they'd enforce it unless a wreck resulted.