In article <4cp9h5$276@brickbat.mindspring.com>, hsilver@atl.mindspring.com says...

>If you want overexposed negatives, you adjust the iso lower to give a
>more dense negative. This is a technique to achieve a print with more
>contrast. Both colour and B/W.

Hmmm.... Depends on what you mean by "contrast". Contrast describes
the amount of difference between adjacent tones, as in photos which have larger changes between tones have higher contrast. One hears
little about "brilliance" these days, which describes the tonal
limits, as in photos with whiter whites and blacker blacks have
greater brilliance. Overexposing negatives produces greater density
range (up to a point), which can improve marginal briliance in the prints, but moves the whole negative tonal scale up toward the
highlight shoulder, which is (uh) rounded (no longer linear). This causes lower contrast (first in the highlights, and later, with more overexposure, in the mid-tones). So, overexposing negatives (both
B & W and color) can result in slightly increased print brilliance
(and shadow contrast, as the bottom end of the tonal range is moved
up away from the rounded [non-linear] toe), while reducing highlight
contrast (often desireable, to make highlights more printable).
I like good blacks (and shadow detail) in prints, so I generally give
negative color a bit of extra exposure (by rating the film 1/3 - 1
stop slower [as you said], depending on the particular film. I rate
B & W normally for the developer used, and adjust development to
provide the brilliance needed for the particular paper I use.
Hope This Helps