Short answer is 1 mist coat
The consumer needs to also consider what
brand of paint they are using & from where they purchase!
As professionals we use Trade quality paint which has more coverage than retail & own brand paint purchased in a Diy store.
Think of the location of the area being painted?
If a high traffic area it would need a more durable paint that can withstand a good scrub.
If say a bedroom then a simple Vinyl Matt is fine.
if the area has a lot of steam & moisture like a bathroom ceiling then a steam proof & mould resistant paint should be used.
also think of the sheen level - for example a Matt finish wonít show as much irregular plastering
a high sheen will highlight every defect.
Strong colours will require additional coats
donít scrimp on buying cheep rollers & brushes
buy good quality - this in turn will help achieve a good finish......
And always wet new brushes & rollers and spin & shake out excess water
this allows faster paint pick up & release