Paraffin is great for removing oily, greasy muck from steel-based motive componentry and is less dangerous than petrol which also cleans well.
If I ever feel the need to clean the chain of any of my bikes, I'd soak it overnight in paraffin then use my current favourite lubricant, 'Purple Extreme' which, although a little pricey, does seem to last well and manifests its properties in improved gear changing on derailleur systems. Thus far, I haven't identified any need! High-mileage riders and those having to regularly traverse gritty terrain might have greater cause though.
The crud which tends to build up on the visible parts of the chain is less than with regular bike oils and cleans off much more easily. In my experience, the worst thing for chains is sand and it's surprising how much attaches itself to the oily chain surfaces in any areas of sandy soil, much of it just windblown. I try to avoid riding on even the compacted sand in beach areas for that reason.
Having said all that, a replacement chain is a relatively inexpensive part of maintenance, especially given the important job it does so I don't think anyone should get too anal about best practice for deep-cleaning bicycle chains.
Tom
