There are a lot of really experienced folks here commenting with more authority on the subject than I can give. With that said, I'm currently in Phase 3 so figured I'd share my take so take it for what it's worth. Like others have mentioned, I don't think you miss anything by going to IFT. In fact, there is a lot of downside to include:
1) exposing yourself to needless elimination. This happened to a buddy of mine who I thought would have had no problem getting through T6s, really sharp guy with a good attitude and apparently decent flying ability who just ran into some bad luck on a few consecutive rides in Pueblo. Poof - pilot slot gone in an instant flying a composite-airframe lawnmower.
2) Having to endure what is effectively a giant fraternity haze (aka the "kick in the nuts" people talk about) for longer than you need to...you will get plenty of it in T6s (and T38s if you go that route). You would rather show up fresh to T6s ready to kick ass than risk getting all burnt out early. Like others have said attitude is so much of the game...
3) delaying your training by getting stuck in "waiting for orders" land. Some of these guys sit on casual waiting for months to go, when all you have to do is show up to UPT and start the grind with your PPL. Along those same lines, any sort of injury (for example having too much of a party with your pals in Pueblo and getting hurt) exposes you to even more delays in your training. It can happen in UPT as well, but why risk it with yet another opportunity in the pipeline to get set back.
Really the only thing you might get from the IFT experience based on what I heard from my classmates who went is the procedural stuff (learning to recite bold face or do stand up in front of a crowd, getting up at 5AM to do formal brief, reporting to fly, MATL, etc...) But you will learn all of that in your first week in T6s anyways! That's what happened to me and I didn't feel behind because of not going to IFT. Don't get me wrong, I could still flop on the rocks as I finish up UPT but my guess is if I wash out now it will have nothing to do with not getting to go to IFT. If you are really concerned about being uncurrent, why not go do a BFR to freshen up? Or better yet, hop in a pitts special with a crusty old flier down at your local grass strip and spool up that inner ear fluid in preparation for T6s! In all honesty, IFT or not, unless you have prior HP or turbine time you will likely have the same learning curve as your buddies coming in from IFT.
Anyway that's my completely unqualified 2 cts...feel free to PM if you have any questions about my experience. I'm a guard guy with a PPL, did no go to IFT, did not feel behind or unprivileged because of it. YMMV