I generally have a dedicated R script to generate functions that I manually create to use in a task. So, in the case that rm(list=ls()) needs to be executed, it’d be very annoying to go back to the function creating script to create functions. source() comes to the rescue!
The source() will run the file inside the parentheses without opening it. Then in my case, all the functions will just be created after the source() line.
Using it is pretty easy too; source('file.R')