# Good
max_by <- function(data, var, by) {
  data %>%
    group_by({{ by }}) %>%
    summarise(maximum = max({{ var }}, na.rm = TRUE))
}

# Bad
max_by <- function(data, var, by) {
  data %>%
    group_by({{by}}) %>%
    summarise(maximum = max({{var}}, na.rm = TRUE))
}