You get to pair the 1 + 3 of fantasy basketball together.
The party offering the trade must be in need of rebs / Blks or is looking at upside.
By accepting this trade you'll become competitive (or dominant if you already where) in FT% and lessen your TOs.
You're losing about 5 pts, 4 boards, a block and about .100 FG% however your gaining two players who hit about .800FT% and .470FG% while being top in their positions. You're also decreasing your TOs.
I would accept the trade. Gasol is a top 30 player, CP3 is #3. Your taking proven commodities over upside.
There's no reason NOT to take this trade unless you think you can't be competitive in REBs and BLKs without Dwight. Which shouldn't be the case if your league has any sort of bench because there are a number of players who can help there.
Both shoot over 500, near 800 on FTs, get around 9 - 7 - 1.5 for Pts, Reb, Blks. and Amir gets over a steal a game as well.