Fewer fields scan more easily
A vCard packs your name, company, title, phone, email, and website into one code. The more characters you include, the more modules (the small squares) have to fit in the same area — and the smaller each module gets, the harder it is for a camera to read.
Only the name is required; everything else is optional. Leave a field blank and it isn't written into the code at all, so for something printed as small as a business card, filling in only what you need helps scan reliability. Long job titles and website addresses eat up a surprising number of characters.
Error correction level and print size move together
Raising the error correction level lets the code survive being partly covered or scuffed, but the recovery data takes up room, so a payload as long as a vCard usually ends up with more modules. At a fixed print size that means smaller modules, so a higher level usually means printing larger.
Adding a logo pins error correction to H (the selector locks) because the logo covers the middle of the code. A data-heavy vCard plus a logo gets dense fast, so print a test and scan it with a real phone before committing to a size.
Scanning opens the contacts app directly
Instead of opening a web page, scanning brings up the phone's save-contact screen. The other person reviews the details and taps save — nothing is copied by hand, so no typos creep in.
You can type the phone number with hyphens or spaces; the generator keeps just the digits. If your card will be scanned abroad, add the country code yourself (like +82). The generator preserves a leading + and cleans up the rest of the punctuation, but it won't add a country code for you.