What is changing between having a thin trace and a very wide trace is inductance vs capacitance. The wider and closer a trace is to a reference plane the larger the capacitance will be. There is a lot to know about this (more than simply I vs C) so I would suggest doing some research on the web.
We typically try to use a trace that is the same diameter as an 0402 pad. (about 1mm) Doing this will reduce inconsistancies along transmission line.