Standard location turbos are limited to their size, and the intake has to run under the stock manifold. The largest inlet that bolt-ons have are a 3", and if you look at any 3 inch inlet, it narrows down to fit under the manifold, then widens back out.

Technically, the only disadvantage to a rotated setup is cost. Even if you're running a small turbo, rotated setups make more sense that the intake is basically bolted directly to the turbo. So even small turbos would benefit, but it would be waste to spend that kind of dough on a small turbo.

Rotated turbos aren't limited to their size as much, and the direct inlet allows for larger size inlets and less piping, which lowers restriction.

That's why it's not uncommon to see GT30R dyno plots hit the same peak numbers as a 3" Green, but still have better topend. The larger housing and bigger turbine and compressor wheel allow a GT30R to hit bigger numbers, but the direct 4" inlet helps the spool.

We know the fast spool of the GT30R isn't from the BB CHRA because the GT30R hybrid's don't spool as fast as a 3" Green. In fact, almost all dynoplots show that the BB CHRA does almost nothing for spool. Take the Element GT65 kit for example. It's a thrust bearing 65lb rotated turbo, which is the same size compressor wheel as a Garrett GT35R. The housing is ever so slightly smaller than a GT35R, which does help improve spool. You would think the a slightly smaller housing may be compensated by the BB CHRA of the Garrett turbo, but dynoplots typically show the Element GT65 turbo does spool quite a bit faster than the GT35R.

At the end of the day, it's really cost. Even if you were looking for a 50 trim turbo like a Green, a rotated setup with the same turbo would still yield faster spool because of the direct intake, even if the size is the same as a stock location. However, people usually associate rotated setups to bigger turbos because it's the only way to get turbos that big. They prove to be a much better option than the very large bolt-ons because they yield larger power with the ability to run larger housing turbos, plus they don't take forever to spool because of the direct intake.

The other thing is people get so stuck using IWG's on their setup, and bolt-ons allow people to do so. People who go rotated ALWAYS use external gates, which is another huge improvement.

Basically, if you can afford it, you should go rotated.