When a computer compares two words to decide whether they are equal, it may or may not consider words equal which only differ in case.
This is relevant e.g. with regard to:
Often, computer passwords are case sensitive and computer user names are not, which can be confusing for the unexperienced user. Passwords are often made case sensitive to make them harder to guess, whereas making usernames harder to guess or remember is not an advantage.
It takes more work for a program to ignore case when comparing data, depending on the data being compared. Usually it suffices in text coded in character sets like ASCII or EBCDIC to merely convert the comparand and the data temporarily to one case and then compare, however it becomes far more challenging in a multi-lingual environment, e.g., using Unicode, since case-conversion rules differ between some languages, for example in German there is no uppercase form for the sharp s ("ß).