I'm learning Haskell, and it's not always clear to me when to use a matcher and when to use a guard. For certain scenarios it seems that matchers and guards can be used to achieve essentially the same ends. Are there some rules or heuristics for when it's better to use matches over guards or vice versa? Is one more performant than the other?

To illustrate what I'm getting at, here are a couple of silly examples I cooked up that seem to be equivalent, but one version uses matchers and the other uses guards:

```
listcheck :: [a] -> String
listcheck [] = "List is null :-("
listcheck a = "List is NOT null!!"

listcheck' a
    | null a = "List is null :-("
    | otherwise = "List is NOT null!!"

```

and

```
luckyseven :: Int -> String
luckyseven 7 = "SO LUCKY!"
luckyseven b = "Not so lucky :-/"

luckyseven' c
    | c == 7 = "SO LUCKY!"
luckyseven' c = "Not so lucky :-/"

```

Thanks!