Depending on your current health and genetic disposition, you can/will get away with skipping warm ups.
But within the next 15 years, and maybe as soon as a few years, your body will tell you that a warmup is required.
Hopefully that message won't be in the form of an injury.
When I started S&S 6 weeks ago I didn't take the warmup seriously and I didn't do the other 2 recommended post-practice stretches.
Doing the complete warmup now takes me 6 minutes, and my practice is better for it.
Two weeks ago I started doing the post-practice recommended stretches and both my tissue issues were resolved in one day.
I purchased and downloaded S&S in less than 5 minutes, forgetting temporarily that decades of developed information and 1000's of hours of experience went into the creation of this specific program.
I'm 53yo and a newbie, but I'm injury/pain free and living/loving the S&S program.
I recommend everyone do the program as prescribed. If they don't like the results after 90 days, they should do something else.
If they add to or take away from the program, it's no longer Simple.
Just my $.02