Yes grand sex.
Seems to be a favorite subject.
The true magi uses sex and it's energies to send waves throughout the Universe.

The waves are, of course, sent anyway, but not as focused and so, less effective.
By the millions of people having sex right this moment.

Kama Sutra has many suggestions for the physical maneuvering of sex as well as the work with the Kundalini (generated energy).
The point is far deeper than most people realize or even care to think.

The astral energies that surround each body are mixed as well as the many 'fluids' that make up both the physical and astral planes.
When you get both of these areas exchanging fluids it has a direct effect on the "Causal" nature of things as well.

There is a bonding that goes far beyond the "One night stand" concept.

Now people do not have to nurture this 'bond' but many do.
We are conditioned by our up-bringing to care for, in some way, the person we decide we will have sex with, and actually do.

Many entities are well fed by the nature(s) of the energies and thoughts, fluids and flows of the sexual nature of the human body.
So many entities will be immediate to give their assistance to the actual conquest of the thing and do whatever it takes to get two bodies to have sex with each other.

There are always under lying factors but just look at the way we think, on the whole, we, as a race, think, sex, sex, sex.

Sex has a very high nature within it but ,as humans, we tend to sink to the lower more readily.
That is because it is much easier to relax to the lower as it (sex) begins, for us, in dealing with the physical body and it's euphoric nature(s).

You will find persons that have sex with each other will begin to think, act and even begin to 'look' like the person that they are having sex with.
Commonly over an extended period of time.

Heavy to heavy , beauty to beauty, there are identity factors also that seem to keep this from happening but they are all just individually decided to begin and remain that way.

 Like the thin tall man that weds a short heavy woman.
They decided that they will form this bond as this "Valance" or identity and would accept and be glad with these natures of one another.
Now if the tall thin man begins to get heavy and/or the short heavy woman begins to lose weight.
(Which, by the way, is bound to occur.)
Then the agreed upon reality changes and so the relationship must follow suit.
It does not mean that they will get a divorce, necessarily, but changes of this kind are so very common and obvious.

What does this have to do with Cabala?
You are the sum of your whole. Seems silly but it is not noticed.
The culmination , not only of the one nature, but of the two.

Being more tomorrow than you were yesterday.
Some it makes feel whole and fulfilled and others are left with a sad emptiness.
This would be because their expectations were not met.
 Either by themselves or the other person.

With no expectations there is no anxiety.
 Psychological mainly but with this often comes a physical reaction.

Driving force and creative energy.
Of course, as in nature, the mix, determines the outcome.
The directed intention and knowledge all come into play with sex for the right reasons.

"What is/are the right reason(s)?"

That is left for you to discover for yourself.
 But the knowledge of what you are doing is a great advantage by comparison to people that flit from partner to partner with no other reason than conquest itself.
Or the need to fill the (seeming and self created)  'gap' that is left by "meaningless" relationships.

Many religions promote the idea that it is wrong to have sex, unless it is under strict guide lines.
Their guide lines. It is ok if you do it 'their' way. But a blasphemy if done with any other deviance from "The rules".

I will repeat to make the point that you are mixing fluids and this will cause a reaction.
The focus of the energy. The knowledge of it's use. The intentions of the 'release'.

These are all very important as to the actual, viz able, tangible outcome(s) of the action and act of sex.