In my experience it usually means "crew stunned" and then your shiny tank is just target practice for the opponent... 
Sure, sometimes you get a tank that just won't die. But it's not often enough to invest a lot in unless it's really cheap (my custom Behemoth actually adds armor and ammo - since it costs so little firepower to do it!).
'crew stunned' isn't a permanent condition. In terms of where the crits land, if you're not planning to move it anyway, the bulk of crit rolls ceases to be a major factor, since they land on the motive systems more often than not. It's that expanded critical table that finally gave assault tanks a role besides "Enormous BV sink that costs a lot and lasts a turn or two before dying without doing much."
Prior to Total Warfare, when what we used was BMR(R) without the Munchkin Maxtech book, Assault tanks (3/5 or slower vehicles) were for the most part, worthless against anyone with even an IDEA of what to do about them. to get a TMM better than 1, you have to flank, which degrades your gunnery by 2, and sitting still was suicide, so lots of missing going on from the assault tank, not a lot of hitting, and it was still pretty easy to kill and very easy (relative) to hit-and the kills would go right past the armor because the base location stack had critical locations on it that were major impactors and would kill it.
Oh, and you could FORCE them to move by hitting hte hex they were in with infernoes or flamers. (survival roll or die during the heat phase, and you'd have to do it again the next time if it survived this time).
TW's expanded crit tables and reorganizing hit tables (and removing fires rules) gave Behemoths and Alacorns and other waddling tanks an actual ROLE that they were at least adequate at besides being a BV sink that cost a lot and didn't do much before dying.
That role?
Camping a location and not moving.
because, as I mentioned, most of the critical hits go straight to motive systems, and since you're not moving anyway, all the rest o fthe hits have to wear through the armor-and tanks have fewer locations per ton TO armor.
Meaning those assault bricks could...be bricks, not expensive roman candles.
Really, everyone seems to be so spoiled by the current core rules, they forget the era when you HAD to move your tanks if you wanted them to be actually useful, and camping was a suicide attempt because...
well, you get the idea.
Assault tanks and the heavier VTOLs both became at least viable
sometimes under TW rules, where under BMR(r) your 3/5 tanks and the Yellowjackets (and their slow moving ilk) were a waste of effort and time to use unless you needed to have a
handicap in order to make the match fair to the new guy.
