well obviously i cant name all roles that IT provides to business under the sun.. but i guess i can name some here..
1. inventory systems
2. transactions systems
3. payroll systems
yadayadayada...
basically every existing systems can be computerized. hence when computerized, they can be connected and records can be automated. save time, cost and increases the busines' productivity.
another wud be the internet. with e-commerce, selection, payment n also delivery (if the product is in digitized form) can be done with the help of IT.