Are there any adverse effect to including library/require statements inside of functions that will be called very frequently?

The time used seems rather negligble, but I am calling the function every few minutes and I am wondering if there is any downside to the repetitve require calls?
note that the function is just a personal util and is not being shared. ie, I am the only one using it

Incidentally, any insight as to why library is half as slow as require? I was under the impression they were synonymous. 

  WithREQUIRE <- function(x) {
    require(stringr)
    str_detect(x, "hello")
  }

  WithLIBRARY <- function(x) {
    library(stringr)
    str_detect(x, "hello")
  }

  Without <- function(x) {
    str_detect(x, "hello")
  }

  x <- "goodbye"

  library(rbenchmark)
  benchmark(WithREQUIRE(x), WithLIBRARY(X), Without(x), replications=1e3, order="relative")

  #            test replications elapsed relative user.self sys.self
  #      Without(x)         1000   0.592    1.000     0.262    0.006
  #  WithREQUIRE(x)         1000   0.650    1.098     0.295    0.015
  #  WithLIBRARY(X)         1000   1.359    2.296     0.572    0.024
r require
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