The way Chinese work with time is very different from what we are used to in Western languages.
Generally speaking, the “time specification” itself (last year, yesterday) is often enough to provide us with the time information.
Anyway, there are situations when it is appropriate to “decorate” a verb with a particle (or set it into a particular construction) to specify about what type of past-action are we speaking.
Circumstances of the past action
This topic is also related to change of events, even though that can also take place in the future.