Except if the temp changes, or the altitude changes, or ... etc. etc. the boost will drift, and unless you numb all the deviation codes, you'll eventually throw a code.
Even worse, fueling might start going all over the place too, unless you're really anal about getting fueling right at a variety of WOT boost levels.
The latter isn't as big a deal on wideband 1.8ts, though so we can agree to disagree.
To each his own. I have no problem with people who decide on open loop boost control, as long as they're aware of the downsides.
We're in the Uk Temp changes and elevation aren't really going to play that big a deal in all honesty!
I've attached a file I recently did for an HTA30 that's running 500bhp, completely open loop and solely controlled by KFLDRL. Works really well and can just as easily be setup or smaller turbo's and injectors.