Two reasons to create table alias :
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You have too many tables.
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You have too many columns in your tables.
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You want to work on your own tables.
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You want to use another schema's tables.
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Your tables have difficult names.
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Your tables are too long.
Table aliases serve two main purposes: when working with tables from another schema (qualifying schema names gets tedious), and when tables have long or difficult names that make queries hard to read. Aliases improve query readability and reduce typing. The number of tables or columns alone doesn't dictate alias use.
Table aliases are a shorthand mainly used to make queries more readable or workable. If a table belongs to another schema, you'd otherwise have to prefix every reference with the full schema name — an alias avoids that repetition. Similarly, when a table has a long or awkward name, an alias lets you refer to it with a short, convenient label throughout the query, especially useful in joins and subqueries.