To travel at a given speed, you need to put out a given amount of power. You can either do that by pedalling slowly and putting a lot of pressure on the pedals, or by pedalling faster and putting less pressure on the pedals.
Since the more pressure you put on the pedals, the faster your legs get tired, it's preferable to pedal faster. Within reason.
First of all, there is a limit to how fast you can comfortably pedal. And second, spinning generally stresses your aerobic system more, so you can run out of breath more easily.
So high cadence isn't somewhere you always want to go, but it's a useful tool to have in your arsenal. And if you can ride smoothly at a high cadence, you will be able to ride smoothly at a lower cadence, which is a good thing.
You may have come across suggestions to aim for riding at 90 RPM. I'm going to make a different suggestion. If you are willing to work at it now and then, you can expand your RPM range all the way up to 120 RPM, and beyond.
To make good progress, you need to do focused drills that will work on your speed. Here's the one that I like to do:
Start at a comfortable cadence and a middle amount of pressure
Over 30 seconds, gradually increase your cadence until you reach the point where your stroke becomes jerky or you start bouncing
Back off the cadence slightly until you are smooth again
Continue for 30 seconds
Slow back down to your original cadence
Repeat this a couple of times, and you're done for the day. The next time you get back to it, extend step 4 to a minute, and then ultimately aim for 2 minutes. You are retraining your neuromusclar system, and it will take a bit of time to do so, but over time you'll smooth out again. Initially you will be a bit inefficient at this, so you might get out of breath. You can deal with this by going into a slightly easier gear, and over time it will get easier.
On normal rides, spend some time at a higher-than-normal cadence, but don't try to push up your whole limits.
You don't need a computer that supports cadence to do this, but it does help. With doing these now and then, I pushed my top cadence from 105 RPM up to 120 RPM, and on a ride last year I held 145 RPM for about a minute while pulling at the front of a paceline on a slightly downhill.
Rating: Good stuff. Will make you faster, but most importantly, will make you smoother and impress you're riding buddies.