Can anyone give me a brief summary of what the benefits are?
It gives you a number to look at
Some people prefer to use this instead of RPE (relative percieved effort) which is where you set the pace based on how hard you percieve it (holding a conversation but breathign hard, out of breath and single words, etc etc). So it's more accurate than that for defining 'zones'. But HR drifts over time with warming up, tiredness, the weather, caffine, recovery from the last session, etc and lags behind what you're doing (eg a 100m sprint, you might cross the finish line and your heart still be beating at the same rate as it was during your warmup).
The better option is a power meter, but a £20 HR monitor is adequate for Average Joe, when a powermeter starts at £600.
Pick up just about any cycling trainng guide and it'll have chapter after chapter devoted to training on heart rate.
I found this to be a good source of information.
http://www.trainingbible.com/joesblog/2009/11/quick-guide-to-setting-zones.html
RPE is Rating of Percieved Exertion.
The benefits will depend greatly on your goals?
For me it means shorter more effective training. I can accurately target the effort/load. So on an interval session I can confirm Im at 90-100% or zone 5 effort for the required time. Yes there is lag changes over time but thats why you use a zone.
HRM is for me the most cost effective option when its linked to uploading the data in to the free online training diary. I can then track training and identify performance increases, rest sessions, weight changes speed distance. Also handy for setting goals. I use a Polar HRM.