The answer to this question may be simple or obvious. Please accomodate me none the less.

I commute about town on my bike. I ride between 120 and 150 miles a week.

Some bicycle computers have cadence meters while others do not.

Question: How would a cadence meter benefit someone who commutes?

I will use this information since I will be purchasing a bicycle computer in the next couple of days.

It probably wouldn't.

It's mainly for those who are training and really trying to use the info to improve their performance.

I kept having problems with my old comptuer that had cadence. When it finally died I got a bike computer that I felt was much better, has a few other features except for cadence and I'm much happier. I only ride for health/weight loss, so I quit worrying about cadence.

I started using a cycle computer with cadence just so I can see at what cadence my body feels the best and gives me the best performance. I noticed that at about 85 rpm I ride pretty efficiently.

Think of it as a tachometer to help you know when to shift. Like driving a stick shift car you can certainly ride a bicycle without one. Your performance may improve marginally if you use it this way even for commuting.

interesting Retro Grouch. So let's say I pick a number to use as my cadence, 85. When I start hitting 86, 87, 88, and so on I should shift to a harder gear?

Cadence is good for someone whos trainign.
Cadence is also good for someone whos new and trying to learn good habits early.

Natural tendancy for new cyclists is to pedal big gears at a low cadence, like 65-70. THats hard on the knees and not very body efficient. A high cadence 85-100 is much easier on the body, but not a 'natural' feel when you first start.

Once you've learned a high cadence, and begin to pedal it naturally without needing to be told to pedal faster, you dont need a cadence meter....since once learned you never forget...kinda like riding a bike.

For commuting it's just a gadget. When (if) I get a nice CX bike this spring my hardtail will get a cheap and durable wired comp w/o cadence and the one on my commuter will move to the CX. As for shifting: shift when you feel the need. That alone seems every bit as reliable as my computer. My shift point is 106-109 with or without it.

Right to the point. Also like a tach, for most non-performance riders it is marginal. But only most. IF you find that someof the time you are shifting too late then a cadence might be worthwhile for you. But even in this case you might want to just try paying extra attention for a while and see if you develop better habits before you spend the extra money.

I think if you ride enough, you pretty much know what cadence is comfortable for you (even if you don't know what the actual rpm is). Cadence is not that useful for training. I think the best for training is a power meter (expensive), followed by a heart rate monitor.

My feeling is that cadence monitors are mostly useless unless you're doing very specific training for racing that requires precise real-time monitoring. For anyone else who needs or wants to know cadence, it's easy enough to simply count pedal revolutions. Once you settle on a target cadence and have spent enough time spinning at your target, you'll be able to maintain it by feel.

Here's my take. As an immediate preformance enhancment you are going to be disapointed but it's not entirely useless for a commuter if you are looking to build more speed or range, or improve your fitness. The same would go for a HRM.

For your day to day riding gear selection/cadence is probably best done by paying attention to yourself not guages. I generally find that it is time to shift to a higher gear when I'm spinning fast enough that I start to breath too hard. Generally I will use as low a gear I can without winding myself. I know for sure that I am in too high of a gear if I can feel it in my legs.

Where these points are comes with a little experience, a HRM can help you get a feel for them. I found that there is a maximum heart rate which I can maintain for a long time and by paying attention I can take myself up to that point and stay close to it even without the HRM. This translates into maximum preformance/quickest times between two points and the most range. A HRM can also help you get a feel for how easy you need to take it occasionally for best recovery.

Cadence will tell you how fast your legs are moving. You can read up and find out what recommended cadences are but you will probably not be able to maintain the most efficient rates unless you have trained yourself to do it. The main benifits you will be get from a guage is help in maintaining a consistent cadence and an easy way to know your average cadence which which you may want to raise over time.

Recording HR, cadence, speed distance, etc. periodically gives you a measure of how you're doing.