You save some $. sure.

But do you really want to wait for 6 months to know your I140 is approved? And then wait for I485 to get approved?

My case:
I140 and 485 premium processing concurrent.
I140 approved in 12th day.
I485 approved in 42nd day,
got Green Card in 49th day. ( yes calendar days )

from my experience, i could hardly wait for those 12 days to find out I140 got approved. Although my case was solid, I have heard of I140 rejected and RFEs so its not over till I140 is approved. There is a lot of validation and I think, FBI background checking stuff that goes on for I140 processing and 485.

If you are 100% sure that your I140 will be approved and you are one of those people who would not waste time checking status of your I140 in the USCIS portal every day or think of it, then NOT doing premium for I140 makes sense. Everything's got time and it will come someday , hopefully. But if this thing worries you as hell and you would be thinking about it every single day, don't you think that peace of mind ( for 6 long months ) is worth more than the PP free $1250ish.

In my opinion, Premium processing is a no brainer. I've seen people doing this mistake of not doing PP and waiting in desperation for I140 to approve. Especially if you have plans to do things within a certain duration.

It all depends on what you care much some few $$ OR waiting 6 months in desperation.

I also feel if you get GC faster you make up that money in no time.

Only if your case is weak I suggest not to do PP and get RFE.

My $0.2.