ABC or Always Be Closing implies a strategy that basically says everything a sales agent does is to work towards a single goal i.e to close a deal. This actually says that if a sales agent fails to close a deal, then all the work they put in was a failure. This is more of a motivational phrase to encourage sales agents to close more deals.
As mentioned above it is used to motivate salespeople to close more deals and acquire more customers.
It acts as a catalyst in improving sales performance and overall business growth.