As you might already aware that continuous Software testing comes under Agile or DevOps approaches.
In this approach, tester can test the functions as soon as developer make the change in code and those changes are merged/available on test environment,which are supposed to be developed in that specific sprint.
So testing team does not have to wait till the end of the build which was the case earlier with waterfall model.
So if there is any bug or improvements are needed in those functions, that can get rectify early which in the end reduces the cost.
Also, this approach helps when requirements from clients are not fixed and have possibilities of change in between.