Hand pump as a back-up.... YES! But many more reasons to have one laying around I think.
If you are prepper minded then its a must, being able to refill your guns without electricity is just smart.
Workout, it will always be a good workout and healthier then a compressor. and if you have extended family like grandkids and nephews and they want to shoot your guns get them on that pump so they learn the value of Work = Reward and gets them active doing something.
Mobile fill station. I just bought a Yong Heng compressor but sadly its not portable and many of the reviews I looked at for the portable 12volt ones said they are prone to issues, have super slow fill times, and are just not built as well as the standard 120 volt compressors. With a hand pump you always have a mobile fill station, going camping for the weekend? Take your bottles and pump and if you run out of air get one of your kids or nephews on that pump lol.
And one of the most important reasons is when one of your friends see your cool PCP gun and wants his own you can lend him your pump till he gets his compressors and bottles purchased. That way he isn't at your house every weekend treating your garage like his fill station lol. But seriously that can help someone else get into PCP, I think the #1 factor keeping people out of PCP is the overall cost of everything.
I think another thing is if you ever want to sell one of your PCP rifles including a pump might be a good thing and more enticing to a buyer as to him its a complete package and will get him shooting that same day.
I bought my pump used from the amazon warehouse store for $36, the liquid air pressure gauge built into the pump is stuck at 2,000 psi, so that's why I got it so cheap I guess, but it works great and is worth every penny of the $36.