The scoring in Three-Handed Whist can be somewhat confusing.

At the start you decide whether or not to look at the Widow. That comes into play later. Then you play to get the most tricks that you can as you normally would. When the hand is over you have your tricks- for the sake of this let's say you won 5 tricks which would equal 5 points. Then, if you even looked at the Widow back at the beginning of the hand [ it doesn't matter if you took it ] 4 points are subtracted and you end up with 1 point. If you didn't look at the Widow, then 3 points are subtracted leaving you with 2 points. Your goal is to reach 15 or more points.

If you have a weak hand and you only take 2 tricks [2 points] after looking at the Widow you end up with -2 [negative 2] points. If you didn't look at it then you end up with -1 [negative 1]. However, and this is important, your overall score cannot dip below zero.

It is always in your interest to play for the most tricks. If you believe you can take 5 or more tricks with the hand you're dealt, it most likely is not worth your while to even look at the Widow.

But it's worth noting that it really only costs you one more point to look at the Widow, so if you have a marginal hand it's quite possible that the look is worthwhile.