What does added rod guides do? For example, 8 guides on a rod vs 10 guides on a rod?

More guides equal less flat spots in the line when the rod bends, more sensitivity, and added casting distance(not extremely noticeable though).

More is not necessarily better, but too few hamper performance. The goal is to have the line path match the blank's bend as closely as possible using the minimum number of guides. Micro guides on a casting rod sometimes require a few extra due to the low height, but some use more than need because they are unnecessarily concenrned about the line touching the blank while landing fish. As long as the line does not go below the blank, no harm is done by the line touching when the rod is heavily loaded.

i agree more or less with dvt.. to few isnt good but to many isnt whats it made out to be either, to each his own on the subject...

if i was selling you guides id tell you more though... you need 1 guide for every inch of rod LOL