A common comment that I see made about R's integer type is that it's only really intended for communication with C code. Do any statement like this appear in any official part of R's documentation? I often catch myself making vectors like integer(10) under the impression that they'll be more efficient for my purposes, only to remember this folklore and reconsider if I should ever be using integers for code that never tries to communicate with C code.
I don't think so. This folklore probably comes from the fact that R is pretty loose about typing and coercion, so it's easy to end up with a floating-point variable by accident.
Integer types certainly save memory:
> object.size(seq(1e8))
400000048 bytes
> object.size(seq(1e8)+0.1)
800000048 bytes
I haven't tried benchmarking to see if R uses faster routines for integer vs floating-point arithmetic, but you could.
I haven't looked carefully through all of R's documentation, but the only slightly relevant comment that turns up in a full-text search for "integer" in the R language definition is:
In most cases,the difference between an integer and a numeric value will be unimportant as R will do the right thing when using the numbers. There are, however, times when we would like to explicitly create an integer value for a constant. We can do this by calling the function
as.integeror using various other techniques ...
I did a grep integer *.texi in the doc/manual directory of the R source tree and didn't (in a quick skim) notice anything else that looked relevant.