Actually, if you go negative in ours, sometimes it works, sometimes it won't. If you use the "desire" column, you get points when the program gives you what you want. If you go "avoid", it gives negative points towards your final score. So, let's say you have "Desire weekends off" set at a 1000 point value (the highest it will go), but you have "Avoid consecutive days >3" at 500 points and "Avoid show times before 1:00 PM" at 700 points. Your max positive score in that case is 4000 (assuming there are four weekends in the month). Your max negative score....wow. For each instance of a 3 day or better, it's gonna take 500 points in the negative, same for each showtime before 1 PM. So, if you got two four days, you're -1000 already. Now, let's flip that and say you DESIRE trips >3 at 500 points. You're not gonna get weekends off. If you get three 3 day trips, that's 1500 points right there, which is gonna outscore you on weekends. Now, if you've got the seniority for BOTH, you'd be at 2500 points, but only the high seniority guys are gonna be able to pull both of those off.
The problem is, we don't know what kind of pairings are out there. If it's all 2 day trips, PBS is straight up going to ignore preferences for 3+ day trips. The pairings don't exist, so there's no way it can honor that preference. The company has been teasing us with offering us access to the pairing generator, but they want WAY to much in exchange. Currently, we can slide our vacation up to four days to match it up with days off, thus extending the vacation longer. They'll give us the pairing generator, but we have to give up vacation slide, which isn't gonna happen. If you know what pairings are out there, you can tweak your PBS settings every month to maximize the chance of getting what you want.