Difference between using `import` with/without the colon

[Jeremy]

Hello, is there any difference at all between the following 
lines, as an example:

```d
import std.regex;
import std.regex : matchFirst;
```

What technical differences does it make (except for having the 
identifier available), using the colon?
Does it make any speed/optimization changes or am I better off 
just importing the whole module?