Spot starting position players can definitely help in four categories, and possibly hurt in one. Streaming starting pitchers can definitely help in two categories, and possibly hurt in two. The no-brainer time to spot start position players is on Monday and Thursday, and day games after night games for your starting catcher and older players. The slight detriment is that the earlier in the week it is, the less you know which category you should focus on.
Streaming starting pitchers on the weekend can absolutely be the correct decision. By then the stats are advanced enough to where you know where you need help.
Going with the poker analogy, running out spot starters against Chris Carpenter definitely creates a hyper-aggressive image.