Depending on how you look at it, a lot of people would think it's time wasting, but there's a tactical side of it.
By passing the ball amongst the backline, you are inviting the opposition to close you down, or to draw them forward, especially if you are leading. They cannot do anything if they don't have the ball, therefore, in passing amongst yourself, even at the backline, would make the opposition come at you, and if it is set right, you could hit them, especially if you have a good passer or a fast runner as they would be pretty high up and closing you down, that could bring another goal or at least threaten their play. This would put doubt into the opposition as to whether to attack you or to sit and wait, but with them going behind or the eagerness to score, they would come again, and then it could happen again, the team launching an attack.
Some of them, when passing between the backline, are sizing up where are the openings to take and see if there's any space for the midfielders to take advantagve of and "hurt" the team. We often hear the commentators say that the team is extremely "patient" when they pass around a lot and ended up scoring. this is because, when you pass around, between the backline and midfield, you are making the opposition midfield chase after you, and if you are like Arsenal, with good first touch and passing, you'll more than likely drag them all over the place, leaving gaping holes here and there for the others to take advantage of. Which also why people say that Arsenal are playing beautiful football, it's actually simple pass and move that drags people out of position for your team mate to capitalise.
The problem with a lot of teams is that they are either not patient enough to pass around and draw the opposition forward, resulting in them passing back to the keeper to hoof it up, which throws the ball into a 50 - 50 position which they might or might not win. Or they are not good enough to pass around when pressured, you just have to look at the way the Man Utd players hassle the backline of the opposition of how Torres or Ian Rush harrass the opposition defenders to put pressure on them, often getting the reward when the defence panicked or misplace a pass or had a bad first touch. We often term this as defending from the front, but it's a bit of a pressure that hope they screw up and get an easy goal.
There are teams who pass around in the last 5 mintues to wind down the clock, but it is a pretty risky thing to do, why would you want to draw the opposition to come at you when they would probabaly throw everyone forward (especially if it's a big game or cup final)? There will be players who would be shadowing every of your move, closing you down while you protect that slender lead, wouldn't it be better to bring the ball to the opposition corner flag where you can play "monkey" there and if you concede the possession, there are plenty of cover rather than the poor keeper? Even better, you might get a corner which you could try and kill the game off.
So to me, I don't think passing between the backline is a time wasting thing, rather a tactical move adopted by a lot of teams, but at times badly executed. it's either that or in some cases when the person in possession is Djimi Traore, have not got a clue on what to do with it, therefore, knocking it to a fellow defender to let him think.