It's not really about impact, but about context. If someone writes something that turns out to be obviously wrong, given the time-period, you could excuse them -- quite a few great physicists come to mind. Without that information, you might mistake them for an idiot. Or it can make a work even more impressive given the limited knowledge of that time-period.

Dates can also help when someone is talking about a technology which might have iterated past the point that their article is even relevant.

Language is very much context-dependent. Providing less context usually only helps misunderstandings.