My wife and I started out insisting that our eBikes had throttles. Part of this was as a safety issue, as a way to get going quickly enough when waiting for a break in cross-traffic and then getting going to cross merge-in. Part was also just the convenience of getting going with a heavy bike, especially on an uphill. For a hub-powered bike, it gets you out of jams - some admittingly caused by rider inexperience. For instance, encountering a hill when you're in a too-high gear, the throttle can get the hub motor going while you downshift into an appropriate gear.
This was our experience renting RadPower bikes for a few months (!) while we test rode other bikes to see what we really wanted. I test rode a R&M SuperDelite up a steep hill San Francisco and was surprised how well it did - but I did have to use my analog bike experience to choose the right gear and PAS level (TURBO!) ahead of time, as well as do my fair share of pedaling. I would have liked a throttle, but felt that I could live without it. However, my wife - a less experienced bike rider - had major issues on the R&M Homage, even with the twist shifting Nuvinci IGH. She'd be rolling along in a high-ish gear and not remember to down-shift as she came to a stop at a light. Then when the light changed, she was in a too-high gear and had a tough time getting going - she even had some scary balance instability. The helpful salesperson at the LBS there did take the time to work with her on what to do, but even so, she ended up insisting to me afterwards that her bike had to have a throttle for safety.
Now, throttles are less useful on a mid-drive bike, since the motor power goes through the gearing, and so if you're in the wrong gear and hit the throttle you might end up with the chain skipping or even overheat the motor or otherwise damage the chain/drivetrain. The throttle won't help you out with a mid-drive as simply as it does with a hub-motor. Some mid-drive bikes with throttles don't include throttles on the high power optioned versions. Although, it looks like the Bafang mid-drives have a Throttle setting page that could be used to slow the ramp-up and even limit the total power it can apply. There might be a happy medium there.
We did buy high-power bikes with throttles. Neither my wife nor I ride the throttle for anything other than short-lived specific situations, but we do like having them there. The more we ride the more comfortable my wife gets on her bike and I believe she'll be using the throttle less and less.
TL;DR
If you're testing bikes without throttles doing the kind of riding you expect to do and have to ask why a throttle, you don't need a throttle. They're easy to disconnect and pull off, btw.
