You're old and confused
The size between pins must be the same. This is known as the pitch and it must match the sprocket and driver.
The difference is that a regular chain has an inner link, then an outer link and so on. A halflink chain has neither, or both depending on which way you look at it. So if you want to lengthen or shorten your regular chain you need to add/remove 1.5 links at a time, but with a halflink you just add/remove a single link each time - so better adjustablility
