It all comes down to "is it worth it?"
If there is something faint you think you can reveal with a longer exposure, or as Fred shows us
you want to squeak the most out of your processing/sharpening, then long exposures is certainly the go, no question, sure it is harder the less automated and/or smaller your equipment (
)...but thinking that long exposures should be the norm and if you aren't doing them then somehow you aren't producing something good...is quite frankly, missing the point of our hobby and as Ray has shown, plucking arbitrary exposure times of 20 or 30hrs out of thin air is kinda meaningless really in the scheme of things...that's my take anyway
Mike