What utm_source actually is
utm_source is one of the campaign tags a marketer adds by hand, and it answers one question: which property sent this visitor. Typical values are newsletter, facebook, google, or a partner's name. Unlike a click ID, it carries no information about you personally. It is a folder label, chosen by whoever built the link, and it will be identical for everyone who clicks that link.
It travels with siblings: utm_medium (the channel type, like cpc or email), utm_campaign (the campaign name you group by), utm_term (usually the paid keyword) and utm_content (which creative or placement).
The mistake that ruins reports
Analytics tools group by the exact string, and the comparison is case sensitive. Facebook, facebook and fb are three separate sources, so a single campaign quietly becomes three rows that each look a third as successful as reality. The same happens with spaces, which become %20 in the URL and read badly in every report afterwards.
The fix is consistency rather than cleverness: lowercase everything, use hyphens instead of spaces, and pick one spelling per source forever. Our UTM builder helps with exactly that: it warns about uppercase letters and spaces, and checks each value against the ones you have saved before, flagging near-duplicates as you type.
Is it safe to remove?
Yes, and it changes nothing about the page. Removing campaign tags only affects the sender's ability to attribute your visit. Since utm_source identifies a campaign rather than a person, it is the least invasive family of parameters you will find on a link.