Preventive Dips VS Quarantine Tank

[nmhs2]

Ok so I was thinking it over. If you get a fish from your LFS and dont want to put it in the main tank due to effects of ich contaminating main tank etc, why waste your time Quarantining for weeks when you can give it a dip? So now the factor of ich or undesirable parasited entering your main tank in factored out the only remaining problem is that the fish could die due to stess of the whole process (salinity change?). What i'm asking is can you get away with just dipping your fish in a formaldehyde/freshwater bath instead of quarantining as far as spreading ich goes?