We completely removed the 'during-taxi' checks and I can tell you it's a lot better.
While doing after-start checks before taxi you are able to really pay attention at the check items ( how many times you responded check,while taxiing,when you were actually looking out and thinking 'what's going on with that truck?')
Also we were able to discover some minor problems before leaving the apron (imagine in LHR to ask,while half-way to rwy ,to return to stand due to..i.e.flaps stuck,..)
In a busy enviroment you are not only taxiing,you also are listening on the freq,maintain situational awareness,knowin who's nr1,who'll stop,who comes from the right...etc (not if you are in some places where they insist on speaking their own language,and you don't know it ).The point is you'd better dedicate 100% atention to that,instead on splitting 50% with the check,and risking not doing any of it perfectlly.
About the fuel burnt...
...there is more to talk..i.e some engines need a time at idle after start,usually 2-3 min..more than enaugh for the after start check,or how much will cost hitting something while checking instruments during taxi (a lot more than the 400 HS was talking about)....