I like that all of my contacts are stored within one app, which is very convenient if you have to switch phones frequently or need access from multiple devices (laptop/ desktop).
Sometimes it can be slow at times when making calls between different offices across Europe. Not many apps support international calling services so this makes things easier! It also reduces costs because there's no roaming fees involved with using an EU SIM card instead of purchasing local data each time we travel internationally. We've been able use our sim cards while travelling without having costly bills sent every month by providers who don't want us as customers anymore after visiting their country once!