My Galaxy S5 is the last Samsung Galaxy with a removable battery. A spare battery that lets me keep a second one charged requires little space change on the phone and allows longer use without portable external battery packs. I've got a charger on the wall at home and a second battery charged when I'm going to go out on the road and need a long amount of phone battery use. Swap the battery when I get down to under 20 percent. Cost of the pair of items was around $16.00.
The phone maker can sell the optional add-ons and batteries can be replaced when they go bad without a professional phone repair outfit having special case cracking tools 8-)
I've had phones that had batteries go bad and swell and get hot. Swap battery and phone is good for a couple of more years.
Why no removable batteries -- they want to limit the lifespan of the phone...
The only thing I don't have on the S5 that's on newer phones was wireless charging which could have been built in.