I rarely avoid carding just so as to avoid cashing for 4, for the reasons which have been explained. But sometimes i will check on a 4 card set if it is enough to cash and make a sweep the next turn (i.e. target is currently on 3) and going to 5 would decrease my chances of survival (eg if all players have 3 cards, so anyone with a 3 card set could take me out). This is definately part of strategy and i have never seen anyone frown upon such a move.
The possibility of turtling on 1 card is a bit more puzling. On another site i play on, as well as giving ponts for second and third place, another difference is the games are 30 seconds per turn. So turtling on 1 card in a bad position is standard practice. On conquerclub there is no prize for 2nd which may explain in part why turtling on 1 card in classic is so rare. However you could win if someone misses a kill (which is why turtling on 1 is most likely better than on 0). On CC a speed game can last for two hours or so, so it is not very satisfying to just sit and do nothing all that time. But this is less of an issue in 24 hour games, since you are not sat waiting in between turns, and if you have many games on the go there is no great psychological aversion to being inactive in one of them. So i would guess that the reason it is rare in 24 hour games this is in part an etiquette thing too.
Missing a turn on 5 seems like cheating to me. In a few situations it can give advantage, i have seen players get winning positions that way in a game or two. However by doing so you are gaining an unfair advantage over those who are unwilling to delay the game in such a way. And as someone pointed out the actual rules of the board game make it impossible to miss.
Unfortunately, I have missed a handful of turns. Not a multitude, but a few. Regardless of whether or not there is an advantage that may arise from this, I am strongly of the opinion that this is not in the realm of defensible strategy. My humble opinion is that you basically make a commitment when you join a game to the other players that basically amounts to an unspoken agreement: You will play as timely as schedule warrants, and you WILL act during your turn unless unusual circumstances prevent it.
Intentionally slipping a turn when a potential benefit is gleaned from this practice is not some form of creative strategizing. It is a back door maneuver, devoid of any shred of honorable gamesmanship, and I'd assert that identifiable patterned behavior of this kind merits some kind of censure or reprimand. Simply...it's inconsiderate to the people you play with. And hijacking the time of others and the enjoyment they get from the game lacks any integrity whatsoever.
As far as deadbeating...I have a hard time understanding how people can do that without feeling some internal derision. I had a player quit after ONE turn lol. Deployed all, attacked a 3, lost 6 troops, and never took another turn. It was almost funny...in a sad sort of way. I'll play with one troop left and try when there is no hope. Seems like the right thing to do.
I believe in playing all my turns (so am against skipping for any reason - just a personal thing), timing out is annoying sometimes (in sequential, I don't like seeing that guy in front has just started his turn and hanging around only to need to wait for an hour).
I can't see any excuse for outright missing a turn in freestyle (just wait for the last minute like everybody else)
taking a turn where you just deploy stack and reinforce but don't attack is fine by me (after all aside from lost troops, this is what happens if you merely fail to conquer anything, and trying to the point of running out is suicidal)
(But what do I know being but a freemium who's only been here a month and a half)