Just because we got Horford does not mean we can ignore the development of our youth.
It also doesn't mean you give valuable roster spots to players that won't contribute to the team this year. Yabusele can develop overseas playing against established professionals. Bentil and Jackson can develop overseas or decide to sign a contract in the D League. You can develop players without having them on the roster. Look at what the C's did with Iverson and Thornton.

Can you please stop using this gif? I have to give you a TP every time I see it
Lol, why is that?
Because it's Nathan Fillion, duh 
My wife collects nerd things like comicbooks and action figures. We go to Comiccons pretty often. She's had her picture taken with or gotten 8x10's signed by a bunch of people she likes. She has a "Captain Wall" where a handful of those pictures hang.
Nathan Fillion - "Captain Reynolds" - Firefly
Patrick Stewart - "Captain Picard" - Star Trek
John Barrowman - "Captain Jack Harkness" - Doctor Who/Torchwood
Edward James Olmos - Technically "Commander" Adama and not a Captain - BSG
A couple weeks ago Isaiah Thomas was at a local sports card shop here in Washington State, so I stopped by and got him to sign an 8x10. I stuck his picture on the Captain Wall, much the chagrin of my wife. Technically, I don't think Thomas has officially been named Captain of the Celtics, but I think he participates in the typical "Captain duties" assigned to NBA team Captains. Also, since I pointed out that Adama is actually a "Commander", I felt Thomas belonged. Coincidentally, as I walked by the "Captain Wall" a couple days ago, I accidentally caused Thomas' picture to fall off. I'm taking it as a sign. Unless Thomas is officially named Captain, he doesn't belong. My wife was right.