Washing paint brushes

depends, if i'm doing a fairly large area I will rinse the brush in water every so often, but then don't properly wash my brush untuill I'm finished that session (in theory, or I might come back for the next session and then decide to try cleaning my brush / walking down the street to buy another one).

if any staining is becoming apparent while painting I will wash the brush, and I don't think it can do you any harm, but that just sounds like one extreme of the approach, with never cleaning your brush at all at the other end. I guess most people would fall somewhere in the middle.