“Grow your audience” is a stretch here. Better to say “...to see where traffic comes from.”
If you want to go a step further and see which traffic sources lead to form completions (like newsletter or app signups), I made a utility that captures UTM parameters and then inserts them into any form submitted during that session: https://github.com/gkogan/sup-save-url-parameters
If you want to go a step further and see which traffic sources lead to form completions (like newsletter or app signups), I made a utility that captures UTM parameters and then inserts them into any form submitted during that session: https://github.com/gkogan/sup-save-url-parameters