I did clearly state in post wildlife in action and other action Its not a rule it is limitation of the technology in question. For example 1/2.3" sensor will struggle to take good low light shots without noise appearing. In some cases the sensor even has noise just above 100ISO. 1/2.3" sensor cannot create de-focus around a subject say shooting a portrait. The are downsides to FF sensor, which is the body can be bulky and more important you need serious glassware for reach. 1" sensors down the line will offer a sweet area between having sensor large enough for reasonable quality and noise at higher ISO. But small enough for keeping lenses on a diet. LOL I am not speaking as if I have not shot with cameras designed around 1/2.3" sensors I have and I soon found their limitations in certain conditions. I then move to a 1/1.5" sensor which produced much improved results. For me personally I like to travel light when shooting. This was from the experience of going digital from film SLR via a bridge camera. Just amazing being able to carry reasonable zoom and fit it in a single pocket or camera bag. So I now keep any kit at 1KG or below.