Before Euro existed, each European country has it’s own currency (French Franc, German Mark, Austrian Schilling, Italian Lira, Spanish Peseta, Portuguese Escudo, Irish Pound, Dutch Guilder, Finnish Markka, etc.). meaning even by crossing the border one has to constantly swap currencies plus inflation. Is that why Euro was created?
Is it because for example, was the German Mark a weak or strong currency? Germany among others adopted Euro in 2002 replacing their own currency. Prior to the adoption of Euro, is it a headache for travelers to swap currencies a lot since each country has it’s own with varying values (volatile whether you’ll end up getting more or losing money).
However there are still EU states that haven’t adopted it today: Poland, Czech Republic, Hungary, Sweden, Romania, not mentioning Denmark (since they opted out) with new states who adopted it recently, that being both Croatia & Bulgaria. It’s weird since despite Bulgaria adopting it, there’s parallel pricing at stores: in Lev and Euro.
Part of the reason was economic: reducing friction in transactions (especially business ones, tourists less so) and creating a currency with a larger economic base and hence greater stability. Part of the reason was ideological: foster international cooperation and interdependence. It was this alliance between conservatives and progressives that led to greater European integration until progress stalled in the early 2000s as both groups lost ground to reactionary movements.
To answer your question: it was a hassle, we had a lot of loose change from various countries lying around the house.