Does the size of XML affect the TRansformation?

This is very important question for us.
We are trying to determine if the performance of a transformation is affected by the size and heirarchy of an XML file.  That is will there be a performance degradation when the size of the XML grows and we need to access data which lies deeper in the heirarchy.
What are the exact reasons performance degrades and how can it be prevented by good programming?
Thanks,

Ashish Tengshe
IT System Analyst

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