this is the old "how long is a piece of string" question.
and the answer, as always, is "it depends"
And what it depends on is what you are trying to achieve artistically, technically and (if you're a professional) financially.
Many, many moons ago I worked as a darkroom tech for a photographic business who's main contract was taking pictures of cars for the local classified ads papers.
Some days the photographers would go out and shoot two hundred budget second hand cars and all I'd do is do a "near enough" print and cut out the background (with a real stainless steel scalpel mind you non of this fancy pants "paths" tool stuff back in '85/86 'ish when Photoshop was just a dim light in Thomas Knoll's subconscious mind). With these jobs the payment per car was so small that I had a limit of 5 minute per car (and in reality a lot less than that, more like 2 minutes per car else I'd be there beyond press deadline)
Other days I'd get a single picture of some expensive performance and/or luxury car and have to spend hours and hours dodging and burning shadows out from off the bonnet or roof and cutting out or inking over heads and faces out from all the the windows that were from all the spectators that would gather around, to use the photographers expression, "like flies to shit" when ever and where ever they would park something like a Ferrari or a Maserati. A job like that would usually get a full page spread that would pay more than a hundred budget cars worth of images and so got as much, or as little editing work as needed to make it totally shmick (err that's local slang for "like a rat with a gold tooth"
![Wink ;)](./images/smilies/icon_wink.gif)
... err as in looking really overly attractive... often above and beyond how good it actually looked in real life... faded paint? no problems we'll burn that back in (or if colour retouch it with ink), naff white wall tyres? I'll make a mask and burn those suckers blacker than coal etc etc etc).