Somewhere along the way a low gear can get too low...like when someone walking passes you trying to spin up the hill
Also if you get too low you will be moving so slow you will fall over. I think the current lowest I have is around the 20" range, much below that is counter productive IMHO. Ditto the insane top end gears. I try to keep my top gears around 100" mark. I am still trying to figure out WTH we need a hundred eleven gears on a tour bike. I can understand having 30 close ratio gears on a racing bike. I did a transcontinental tour in 1977 on a 15 speed bike and judging from the wear on the rear cogs didn't use quite a few of those gears very much.
I also agree with bobfiets...
Found Getting off and pushing is another method..
may be a bit too low tech.
I quite often "tour" on my Raleigh 3 speed, no shame in walking a few hills, it is good for the muscles to stretch and to use a different muscle group for a bit.
Aaron