I'm not an expert on online dating as I only did it for a month 
But for example, when I met my current partner I was talking to him and another guy at the same time.
Because of the way it works you might have 2 (or more) people contact you and start talking to you on the same day.
And lots of people are flaky and chat to you all evening... and then just disappear the next day.
So in my case I had 2 potential dates who I was talking to. But I hadn't met up with either of them yet.
I was hoping that the first guy (now current partner) would ask to meet up but he was taking it slowly.
And the second guy seemed keener and a good match too.
In the end guy 2 flaked on me 3 times (with genuine and then non genuine excuses) and i was very glad I had not stopped talking to guy1, and in the end I asked him out for a coffee.
It would have been a real shame to "miss out" on him for a guy i hadn't even met yet, and who, as it turned out, after a week of intense texting every day, decided I was "too good" for him.
OTOH if I HAD met up with guy 2, I probably WOULD have stopped chatting to guy 1.
But I'm not sure if that would have been a good idea because even if I met him once I couldn't know if he was potentially relationship material or not.
And the only reason I would be with him us because our schedules meant we met first.
I feel there is a bit of a judgy tone about multiple online dating, but I think mostly it is the lack of context which makes it hard to decide whether the person is genuine or not, they could literally be anyone.
@Sparklingbrook you said the exclusivity talk must be cringeworthy.
Not ime. We slept together, on our 3rd date, and then at some point one of us said something about other people and what we were looking for and I said I didn't want to share and that was it. He'd already deleted his online profile by then anyway 