In mysql if table fit into buffer pool is there any benefit to have partition? Lets say I have a table with 100M rows. All table have enough space on buffer pool. So is there any performance or others benefit to create partition on that table? 

NB: Storage engine - InnoDB
If your purge strategy includes time-specific purge eligiblity, partitions could be helpful.  For example, if every quarter, you will purge everything over 5 years old, it will be in your best interest to have a quarterly data table plan in place.  Taking a table out of service is quicker/cleaner than DELeting a quarter's worth of data rows.  innodb_file_per_table=ON will be needed to be effective.  Filenames need to represent the datacontent, such as 2018Q1, 2018Q2 etc or possibly 2018W01 - W53 if you want calendar weeks to be able to purge.  Dream big, plan carefully.

For alternative to simple filenaming strategy as above,  

Read more on: http://mysql.rjweb.org/doc.php/partitionmaint