When I was looking at this post by one of the long war crew, they said specifically
I've done 5-6 smash and grabs so far in my rookie run through, and none of them have yielded any elerium or supplies even though I grabbed all 4-5 crates every time. Maybe it's just bad rng, but I was expecting a "primary source of elerium and major source of supplies" and have not found that to be the case. I have indeed gotten alloys every time and a bunch of other random items, but I still find that troop column/supply raids are vastly preferable, profitable, and and desirable for farming elerium/supplies.Smash & Grab
The new mission type for 1.3, these are going to be your primary source of alloys and elerium and a major source of supplies. Unlike other timed missions, the reinforcements won’t start dropping until the timer runs out, but once it does they’ll be dropping every turn. S&Gs are moderately difficult, harder than Troop Columns but easier than Supply Raids. As with Extracts, you start these missions without concealment, meaning that a scout with the Phantom ability is useful.
What determines the the S&G availability? While in the early game (pre-october) I regularly saw these missions, this entire past 2 months of November and October I have seen none at all. I have 2 regions at Strength 3, both with 13 rebels on intel, and although I've been flooded with counter ops/troop ambushes/hack missions/supply raids left and right, I haven't seen any S&G. Is it just bad RNG or something?
Overall I love the mission type, although I still feel like troop ambushes/supply raids seem to be more rewarding and desirable overall since they give more elerium/alloys and also reduce strength in the world.