A spreadsheet can work for a small shared budget, but it breaks down when people forget to update it, use different formulas, lose receipts, or need to settle while traveling. An expense splitting app is better when the group needs speed and trust.
Spreadsheets require too much discipline
Someone has to maintain columns, formulas, currencies, categories, and payment status. If the spreadsheet owner gets busy, the system usually stops being updated.
Apps are better for mobile moments
Most shared expenses happen away from a laptop: dinner, groceries, taxis, hotels, wedding appointments, and group activities. A mobile-first app lets people add the cost while the context is fresh.
Use a spreadsheet only for deep analysis
Spreadsheets are still useful for detailed exports and personal analysis. For daily shared spending, the primary ledger should be simple enough that everyone participates.