Cavs only pursue this trade if they decide to cut long term salary to avoid the 2nd apron. Mobley would shift to full time C and Rui fits in as starting stretch PF. Knecht is the rookie prospect on a controlled deal.
Lakers get a starting caliber C who is a lob threat and can defend the rim. Allen's salary signifcantly jumps from $20M to $28M, $30M, $32M in the following years.
If salary savings is what Cavs are looking for, Lakers have other expiring contracts they can use to absorb more salary (e.g. Okoro 2 years for expiring contracts of Kleber or Gabe).