This type of 'officiating' is common in only in govt/semi govt & PSUs. Not many in Pvt.sector. This connotes nothing but a temporary arrangement till a permanent incumbent takes charge of a vacant position. The reason for causing a vacancy notwithstanding, an employee either of the same cadre or immediate junior could be posted or asked to perform the duties of an official. Many a time this arrangement is necessitated due to a present incumbent 's absence like going on leave, mostly a longer duration on a/c of sickness, deputation/trips to abroad etc. Some times the 'officiating officer' may be paid an 'officiating allow' either equivalent to the remuneration (diff.) of the post or one increment. Mostly this arrangement can go for a limited period. So far as the aspect of shouldering responsibilities, sharing power vested in the post not likely to change just because they are 'officiating' . Such a person normally reverted back to his original position once the regular/permanent incumbent rejoins in the post he was holding prior to his/her temporary absence.
This arrangement call for an official order/formal communication to give effect to.
In some estts this arrangement is also called as 'Acting'.
27th June 2019 From India, Bangalore