Charles Ellicott Commentary 2 Chronicles 29:35

"And also the burnt-offerings were in abundance, with the fat of the peace-offerings, and with the drink-offerings for every burnt-offering. So the service of the house of Jehovah was set in order." — 2 Chronicles 29:35 (ASV)

And also the burnt offerings were in abundance. — Another reason why the Levites helped the priests: the latter were so much occupied with the actual service of the altar.

The fat of the peace (thank) offerings — which had to be burned upon the burnt offerings (Leviticus 3:5; Leviticus 6:5).

And the drink offerings. —Numbers 15:1–16.