Umair Shahid explains the benefit of Heap-Only Tuples in PostgreSQL:
Heap-only tuples, also known as HOT, are PostgreSQL’s answer to the update query performance issues caused by MVCC. These tuples allow PostgreSQL to mark a row as “dead” and physically reuse the space it occupies in the table. This process eliminates the need to keep multiple versions of the same row, reducing I/O and improving query performance.
Read on to see how these compare to the normal MVCC process in Postgres, as well as cases when you should and should not use them.