[R] POSIXlt vs POSIXct

[Steven R Corsi]

Hello R users

I am searching for a descriptive summary of the use of POSIXlt as 
compared to POSIXct date/time formats. I have been using them 
extensively for different purposes, but still can't quite understand 
when to use which one for the most efficient coding and use. I typically 
use them in graphics, comparison of times, interpolation of values 
between times, computation of time-series parameters, and so on.

My request is simply to learn if there is a resource out there that 
explains the strengths of the use of each format in different situations 
and if certain situations require one over the other. My web searches 
have turned up basic things like the vector form (POSIXlt) vs the 
decimal form (POSIXct), but I could not find specific guidance to 
understand when it is best to use one over the other.

Thanks
Steve