Benefit of using WITH (TABLOCK, XLOCK) when inserting one line in a table?
Exclusive Access or Increased Performance

From what I've seen, this "could be" someone's attempt to make sure that absolutely no one else enters identical rows, that you're inserting, into the table. 

Or if it's mass inserts, it can save time and have minimal logging.

https://drillchina.wordpress.com/2012/12/18/use-tablock-to-boost-your-insert-into-select-performance/