Is there a reason/benefit I am not aware of for this kind setup? I now manage a MySQL database that was designed and created by another.

I am confused about a certain setup that the original developer created..

He did not use auto increments for table IDs. Instead, he created a table called
system_sequences which has two columns:

system_sequences.Table_Name 
system_sequences.Next_Value


Here is an example of a table and how it currently inserts into the table (try my best):

there is a table called customer with an unique ID column.

If I want to insert into customer, currently I have to do the following:

SELECT system_sequences.Next_Value 
FROM system_sequences 
WHERE system_sequences.Table_Name = 'customer'


save the next_value into a variable and use it as the next ID for customer

then I have to:

UPDATE system_sequences 
SET Next_Value = Next_Value + 1 
WHERE system_sequences.Table_Name = 'customer'


I did not design this, I do not like it in any way shape or form  ( I actually hate it ) and I want to convert everything carefully to auto_increment

But is there a reason for this or a benefit that I am not aware of? I have never seen anything like it before. And there is no documentation for this database that explains anything.
I don't know about mysql but in SQL server, you would use this type of thing when you can't afford to have gaps in the sequence from rollbacks. Often this is a requirement for invoice numbering for accounting auditing.