Honestly, 9 times out of 10, being able to evaluate swatches early means I'll be spending more. There's the occasional collection bomb for me, but for the most part swatches ADD more "on the fence" things to my list, and remove far less.
I like having enough time to think about how I'll wear the product, what combos would work for me, if I need/want to get something else to go along with a new item I'm thinking about, and it gives me time to convince myself that I can actually pull off some of the new/in trend colors and looks. It gives me confidence, both in my purchases and in my ability to make new stuff work.
For me, not having swatches around early makes the entire MAC experience more stressful and less fun. With the massive amount of collections they release, I need time to consider what I'll be purchasing based on actual product swatches. Without that time I see myself becoming seriously overwhelmed (especially with the huge collections like SCF, etc.) and moving on to other brands more.