I don't believe I would consider them essential....but not far from it. Especially when working with old double rifles for which little data is available. Also, as Mike mentioned, old rifles in general. Those are the two most common uses for me these days. When I was shooting a lot of long range stuff, 500 yards and out to 1000, the data derived was a help in calculating trajectory and from that sight settings. And, it's just plain fun to know what's going on with your load.
My first was a Chrony back when they first came out. I didn't like the screen on the unit because you had to walk down to the unit, or use bino's, and then record your data. I also learned that the Chrony would not survive a direct hit from a 45-120 Sharps cartridge at about 12 feet. I see that the Chrony's of today have recorders remote from the unit, which is an improvement. I don't believe they have overcome a direct hit from a bullet. I replaced it with a Pact and I do like it better. I believe the screens on the Pact are bigger and I like that.
