I use one main phone (Lumia 950XL) and I have a Windows phablet (Lumia 1520) which I use as a tablet when I'm charging my phone. I use my Windows phone like anyone else uses their phone: Phone, calendar, email, text, web, camera, GPS, skype messaging, Wunderlist shared family grocery list, loyalty card wallet, Cortana reminders/searches, Groove music, Pandora radio, Twitter, Youtube, weather, news notifications, alarms, calculator, Microsoft Band (fitness, sleep tracking, weather, notifications, alarms), Fitbit (family competition), USPS mail tracking, Duolingo language learning, etc. So I pretty much use my Lumia for everything all day long, except for gaming which I do on Xbox/PlayStation and for shopping/banking which I do on PC.
Overall I'm happy if not completely dependent on my MS Band and phone. My points of contention with my Windows phone right now are a lack of retail location apps (banks, restaurants, grocery, cinema, etc.), a lack of updates for some old Windows 8 apps (mostly news apps), losing GasBuddy app, very limited credit card support for MS Wallet, a very limited smartwatch and smartphone ecosystem. For the most part I can deal with using the web for apps that are missing, but in aggregate it can become a little annoying if the website is poorly designed (GasBuddy) or requires constant logins.