According to Wikipedia,
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.
However, it's difficult for me to find any resources as to why reducing current flow, or dividing voltages, is useful in the first place. The Wikipedia source came up google searching "Why are resistors useful?" Which only served to explain what they did, but not explain why what they're doing is beneficial. This may be a very basic and trivial question, but I genuinely don't know.