I guess most IMGs study due to a lack of knowledge about - 1. the exam expectations, 2. hospital culture and 3. expected physician mannerisms in US
For American graduates, it is nothing different from what they already did - a cake-walk, but IMGs would need to know how the american docs do it and what to expect on the exam before they feel confident about spending almost $1000 $ flying to US, then taking the $1,200 exam - which happens to be quiet a fortune in most countries due to local currency conversions.
If I were to take an clinical exam in Kenya or Australia or UK- I would definitely need a resource to know how things are done, the local lingo and other minor things before I take it. Would you agree ?