Standard turbos use a thrust bearing design and BB turbos use dual ball bearings to support the center shaft.
There is a difference for the better with a BB turbo. Faster spool up, quicker response back on boost between shifts, longer life, ability to run a larger turbo with less lag than the same or slightly smaller thrust bearing turbo, etc.
The only downsides I can think of are cost (more expensive) and you have to run clean (filtered) oil thru it at lower oil pressure (from the cylinder head).
Some will say they wouldn't run one over a thrust bearing turbo, but if they had their choice without having to pay the difference, they would go BB
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