Here's my take on an explanation of

, in a few parts.
At

, black has various options to settle the two stone group or otherwise use it, but by playing

, black is committing to a certain subset of those. In particular, black is creating a second group and strengthening white. If the rest of your gameplan hinges around starting a big fight here and you think it will be favourable, that's fine though it may be risky. If your plan is to sacrifice the two stones, this may also be playable. However, black must be sure that this is the correct strategy to take for the game.
If black doesn't know what he wants to do with the group after

, or has competing ideas, it may be best to leave it immediately for another part of the game. White needs to play multiple moves to capture it still, and for the time being doing so would be slow, so if white does do that, you can get ahead in the game by playing elsewhere. When black tenukis, the rest of the board will start to develop, and the balance of power around those two stones will change. Later on, black can play to use those stones best with the rest of the board, because all the options are still open. However, if the

,

exchange has been made, there are less options for black, which makes it easier for white to cause all of them to become unfavourable.
For example, later on black may want to attach underneath or on top of the pincering white stone to help settle the black group, but this option is gone now. Black may also want to lean on the right side to build strength and later attack white's pincer. If that's the case, though, maybe the course of the game will make black's counter-pincer look too tight, or it would have been better to cap. Black may also be interested in switching directions, since white's corner has weaknesses right now, and white chose to emphasize the bottom. In that case, J4 may just end up a useless stone that helped white.
This is a somewhat complicated subject, though, that ties in with probes.
Probes are also moves somewhat like this, but the idea is somewhat different: a probe is a move you play when you aren't sure what to do, as you may be in this situation. However, the idea behind a probe is that you're asking your opponent to commit to one or another course of action, which you can then use to plan your next move. A classic example might be to see whether the opponent is going to take the corner or the outside with an enclosure, or to defend the left or right side of a side of the board against a cap. Once the opponent declares their intentions, you can play against that.
With the corner enclosure probe, for example, you can reduce the outside that the opponent has tried to claim, knowing you can live in the corner any time, or you can not worry about it much, knowing that the opponent has given you lots of space and aji for a proper invasion in exchange for the corner territory.
The tricky part is that a probe needs to give a genuine choice and be flexible. If your opponent can defend against it while making himself stronger everywhere, it's just helping them. If you don't have a good followup for later, it may just be a wasted stone.
Some probes can be very clear-cut, while others are much less black and white, good or aji-keshi, and have aspects of both. Some of these engender debate at the highest levels.
To go back to the initial

, it's possible to play moves like this thinking of them as probes, but the onus is on you to show that they are good probes, and not just limiting your options. In this case, however, there is another problem with this move that bears thinking about.
In the bottom and lower left, white has a fairly solid corner and two high extensions from it, giving a posture that implies that white would welcome a fight here. Playing this move with the intention of starting a fight now, before white's right corner gets stronger, is a valid strategy, though maybe black should lean on the corner first. However, when black tenukis, white can take the initiative in the fight, and be splitting two weak black groups with one weak white one, which is naturally unfavourable for black.
Black's tenuki first off would allow white to strengthen his stones for the fight ahead in a very natural manner, if white responded to

directly. Second, with white's actual response, or a slightly tighter one, white is strengthening his corner group to eliminate weaknesses for the coming fight. Black has also locally fallen a move behind in the fight, so he should expect to get a worse result than if he had continued directly.