What does "units" mean in epiR package? From epiR manual for epi.2by2 function:

units: multiplier for prevalence and incidence estimates.

In examples it is set to 100, units=100. What does it mean?
Note: I am working on ~5K case ~5K control data, no stratas, outcome vs exposure - 2by2 tables.
Update: This PDF might be relevant.
 A: One can find the answer to this by digging into some of the examples:

A study was conducted by Feychting et al (1998) comparing cancer
  occurrence among the blind with occurrence among those who were not
  blind but had severe visual impairment. From these data we calculate a
  cancer rate of 136/22050 person-years among the blind compared with
  1709/127650 person-years among those who were visually impaired but
  not blind.

library(epiR)
dat <- as.table(matrix(c(136,22050,1709,127650), nrow = 2, byrow = TRUE))
rval <- epi.2by2(dat = dat, method = "cohort.time", conf.level = 0.90, units = 1000,  homogeneity = "breslow.day", outcome = "as.columns")
summary(rval)$ARe.strata


The incidence rate of cancer was 7.22 cases per 1000 person-years less
  in the blind, compared with those who were not blind but had severe
  visual impairment (90% CI 6.20 to 8.24 cases per 1000 person-years).
  Confidence intervals for this attributable risk estimate are from
  Rothman (2002, p 137).

Essentially, for many rate-based estimates in epidemiology, your estimate is multiplied by some number in order to get something like "Cases per X person-years", as these are often more intelligible than "Small Decimal per 1 person-day" or however else your data is estimated.
In this example, the units = 1000 yields an estimate of -7.22, which would be interpreted as 7.22 less cases per 1000 person-years. Changing units to equal 100 yields -0.72, which is interpreted as 0.72 less cases per 100 person-years.
