It may depend on your water hardness - wikipedia has a decent article on Dishwashers
This tells more than I can...
http://www.dishwasher-care.org.uk/best.html
Rinse Aid is used to help the rinse water to drain off before the dryning cycle starts and bakes any water droplets (and any bits of food debris they contain) hard on the crockery.
The manufactures make provision for Salt, Detergent & Rinse Aid in their machines - they probably do this because they know what they're doing - it would save them money and lead to more sales if they were to leave out the salt and rinse aid compartments but for some reason they continue to include these things. I think it's their way of saying they do not approve of Three-In-One tablets.
Good luck...
Peccavi, July 2009
