Golden BB stories are always out there. I once took a Rifleman X with the two LB10s and on the first shot of the game got a tripple engine TAC on a Stormcrow A. But, I only ever did that once. If I ever did that matchup again, the Stormcrow would rip the poor Rifleman limb from limb.
The idea is that you can shot something, anything, with a BB Gun, the most underpowered sort of gun that you'd ever think of, and that by some freak chance, some 'golden' shot can find the powder magazine of a battleship or the famous 'open maintanence panel' in the front of your Dire Wolf.
Getting back on track, when we talk about the notion of 'late movers' it does depend on game size. In a lance on lance game, 25% of your force moves last when you win int, and depending on how you're positioned that can be as much as 50% of your striking power at that moment, so it can be a big deal. Even in larger games, when you've spread the field, you only have to move after the mechs that you expect to take fire from, and fire at, and you can do this even if you lose int, if you can make your opponent react to you on another part of the field, or do any number of other tricks. Plus, as I spoke about, even when you lose int, you still need to be aware that your opponent will try to work his own brackets, and you need to move with that in mind to prevent it.
Yes, some players don't think about these things. But when the difrent of one hex or two hexes can be a +2 or a -2 TN, these people are easy to gain an advantage on.