Benefits of table partitioning on same disk Maybe is stupid question, but I must ask to be clear with that.

I know that table partitioning is powerful mechanism of speeding data search when partitions is placed on different disks.

What I need to know what I can get if I place partitions on same disk?
It can help query performance by employing partition elimination. This means large sections of big tables can be ignored when looking for values which means much less IO. Index alignment needs to be looked into when partitioning. See details here

You can break your backups by partition. This can be useful if you are struggling to complete your backups in time. See here for details

Index rebuilds can be done at the partition level instead of the whole table.

Large inserts can be done with partition switching.

Queries can also run parallel across partitions.