What’s the purpose of using braces (i.e. {}) for a single-line if or loop?

I’m reading some lecture notes of my C++ lecturer and he wrote the following:

1. Use Indentation // OK
2. Never rely on operator precedence – Always use parentheses // OK
3. Always use a { } block – even for a single line // not OK, why ???
4. Const object on left side of comparison // OK
5. Use unsigned for variables that are >= 0 // nice trick
6. Set Pointer to NULL after deletion – Double delete protection // not bad

The 3rd technique is not clear to me: what would I gain by placing one line in
a { ... }?

For example, take this weird code:

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
{
    if (i % 2 == 0)
    {
        j++;
    }
}

and replace it with:

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
    if (i % 2 == 0)
        j++;

What’s the benefit of using the 1st version?