In xargs.c there is the following code:

  /* Take the size of the environment into account.  */
  if (size_of_environment > posix_arg_size_max)
    {
      bc_ctl.arg_max = 0;
      env_too_big = 1;
    }
  else
    {
      bc_ctl.arg_max = posix_arg_size_max - size_of_environment;
    }

The equivalent code is missing from find.  This means that if
the environment passed to find is too large, it can produce
exec() errors when "{} +" is used:

$ env | wc -c
    1953
$ find . -exec true {} +
$ FOO=$(printf '%1024s' x) env | wc -c
    2982
$ FOO=$(printf '%1024s' x) find . -exec true {} +  
find: true: Argument list too long
find: true: Argument list too long