It's not a bad question, and I have multiple answers:
1)Right now, my jailbroken 128gb 6 is my small pocket moblie phone, my mountain bike/exercise iPod, and in house entertainment hub that splits music through my house via Bluetooth.
My jailbroken 128gb 6s+ is my go-to for mobile entertainment and OIS picture/video taking while I'm out and about(unless I wear tighter clothing).
The jailbroken 64gb iPad mini cellular used to serve as my infotainment/GPS unit on the dash of my old Honda until I sold it, but now stays at the house most of the time now, and is used for watching movies, YouTube, and websites that are much more easier to see/navigate with a tablet.
2) I always keep a back up phone (6), for which will be of use when the 6S Plus gets sold right around the time the 7 will be announced, so I will (hopefully) get top dollar, then use that top dollar towards the next latest/greatest(but not until sales/availability hypes down). Eventually, all my products get cycled out with newer versions when I see fit.
3) Because I can. And, I feel very fortunate and lucky to be able to have, like eyoungren said, options.
I have also tinkered with the idea of picking up an excellent conditioned iPad Air 2 for even bigger viewing at home, but maybe that's a little overkill, ya think?!