In a bash script, I stumbled upon this piece of code:

```sh
opts=${1:+--host $1}
/path/somecmd $opts somesubcmd

```

By testing, I found out that `$opts` expands to `--host $1` whatever `$1` is.  

I wonder what is the purpose of this syntax.
Why not simply use `opts="--host $1"` ?

Is it a specific way to pass options to a command ?