I have a 3yr old and a 4month old. For background, my 3yr old couldnt walk until she was 19months and we dont have a car as we live in London.
For short journeys, she is absolutely fine on a buggy board, but she wouldnt manage a whole day out for example, especially if its on a weekend as she still has a nap on Sat and Sun. Our buggy can convert to a double, so if we know we are out all day (or if i think we need it for a safety perspective such as lots of busy roads to cross), i take it in double mode. Most of the time i have it in single mode eg. Buggy board + bassinet for just pottering to and from the park, supermarket, nursery, etc
In an ideal world, i would have bought a side by side lightweight buggy. But we already have the main buggy plus a travel buggy and i just couldn't justify buying a third!! But also, a lot of the cheap doubles are max 15kg in each seat, which is around 3yrs. For a 22kg or 25kg double, you end up having to spend more, which i really didnt want to do.
So thats a v long way of saying i think it very much depends on your lifestyle, where you live, and how good / sensible the big one is at long walks!