Turbo - Before Throttle vs. After Throttle

What advantages does one have over the other if any?

Only "throttle after turbo" is used, except a few cases which used the throttle before; for example some of the turbocharged F1 engines from the eighties.

I think the purpose of placing the throttle before the turbocharger was to keep the turbocharger up to speed when going off the throttle.
The obvious downside is that the volume that will be put under vacuum is large, giving increased throttle lag. With the throttle before the turbocharger the turbocharger must have a seal that won't leak out oil during vacuum, which a normal turbocharger will do.

Is oil leakage and throttle lag the only problem with a turbo that has the throttle valve before it? Does it pose a significant problem with performance?... if so what are the benefits of having this configuration?

Is oil leakage and throttle lag the only problem with a turbo that has the throttle valve before it? Does it pose a significant problem with performance?... if so what are the benefits of having this configuration?
Oil is leaking due to the vacuum in the compressor with a closed throttle when placed before the turbocharger.

How could I eleminate the issue with the seals as Im interested in building a fast and efficient 4WD MK2 Focus (European)