For emergency purposes; they're a lifesaver.
I'll give you an example. In the recent floods in Binghamton, the cell network was overwhelmed; it crashed a few times, and people were advised to use it only in an emergency. Landline network was functional. Ditto for any major event in the US. I can provide backup statistics for it, if you'd like. On 9/11, even, when we lost a dozen major switching centers, I was able to call into Manhattan on a landline checking on friends and colleagues. The cell network was useless. I can continue stories, including the October storm here, and a dozen other big events....
Cell-on-wheels sites (COWs) are useful, but not always available. Can I ask you how many of my friends called me, when they could, complained, and I said essentially... I warned ya.
VoIP, Cell, and Digital systems all have limitations on 911 service. It's not based on PSTN termination, but on inferred position. Cell service in WNY is good for ~600'. Sounds close, and if you're in a smoldering car, sure it's "good enough." If you're lying on your kitchen floor, it's not. E911 service on any radio service isn't all that good;
In a power failure, your cell, and all cell sites have a service life of ~6 hours. Ike Eisenhower makes the PSTN (Frontier/Verizon, not TW) network have a minimum of 96 hours of generator and battery life (All CO's are equipped for 7 days, in the real world.)
Personally, I'm not that old (35.) I've owned cell phones since I was 18. All telephones put food on my table, and clothes on my back.
I can't stand the half-duplex, oversized walkie-talkie sound all cell phones have. It's a pet peeve. I'm an audio nut, regardless of if it's a stereo, or my phone.
If you're really only using it for emergencies, switch down to Measured Rate service; it'll be around $15/mo plus tax, and still provide you a backup.
We preach it in our hobbies to have a "blanket" of extra pumps, lightbulbs, a hospital tank, etc. When we look at emergency service, our possessions, and our lives we'll always default to the lowest possible cost provider. It's kinda odd.
I do understand the urge to "cut the cord", I just don't think it's long-term prudent. It's just like insurance, you hope to never need it, but when you do, it's irreplaceable.
Just my $.02.....
-Andy