We have been in Europe for a month now. Day 1 we bought SIM cards for both our iPhones. 150GB for Italy and 12 GB for EU outside of Italy. We always use WIFi at lodging. Our sims recharged today, and since we reset cellular statistics, we could tell how much data we used in a month. 3.5Gb for me and 7GB for Tom’s. We use Google maps when driving or walking or transportation directions a lot.
Phone data use is needed more than 5+ years ago - direction for walking and public transportation, buy tickets, show tickets, receive entry instructions for apartments day of, (or texting via WhatsApp to let host know you’ve arrived), QR code menus, looking up hours for places, etc.
Also seems that free public wifi is less available or less advertised. We were meeting Friends in Strasbourg and they spent 30 minutes looking for free wifi to text us on what’s app where to meet.
Spending an hour on day one getting SIM card is well worth it. Ours was 2 phones for 2 months -€80 including activation and Italian phone #.