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.