In some cases, that is something that evolves over time. For instance, "today" and "tomorrow" used to be spelled "to-day" and "to-morrow".
But in general, it helps make the meaning much clearer in what could otherwise be an ambiguous sentence. Yesterday we were re-installing the Windows operating system on an old PC, and during the installation procedure, we both burst out laughing when this message popped up:
"Installing malicious software removal tool..."
There are two ways to interpret this, both with very different meanings. What Microsoft presumably meant to say was "Installing malicious-software removal tool...", meaning a (helpful) tool to remove malicious software.
But without the hyphen, it could just as easily (and just as correctly) be interpreted as "Installing malicious software-removal tool...", meaning a malicious tool that will remove software, most likely in a bad way.
The art of proper hyphen usage is rapidly being lost, which means that I generally have to read posts a few times to figure out what the writers actually meant.