Why P-TTL? Follow-up

[Joseph Tainter]

Lawrence Kwan wrote:

"And in case of *ist, it can give priority in the matrix metering area 
corresponding to the focal point.  Off centered subjects is one example 
where P-TTL should be better."

For this to work I assume one would have to use either the multi-point 
focusing (letting the camera decide what to focus on) or the selected 
point focusing. Using only the central sensor with focus lock on 
something off-center wouldn't work. Am I correct?

Thanks,

Joe