Reflexivo: Se dativo

Question

Could you please explain the below:

Se dativo o intensificador del verbo.
Con el mismo valor: me, te, nos, os.
A veces, el pronombre reflexivo sirve únicamente para intensificar el significado del verbo, en construcciones transitivas o intransitivas. Puede añadir matices significativos, no siempre precisos ni claros.
Se presenta en dos tipos de construcciones

Concordados: la persona del pronombre coincide con el sujeto:
· Comió tres platos. / Se comió tres platos. (Transitiva)
(Here we emphasize what? What tone?)

· Fue en seguida. / Se fue en seguida. (Intransitiva)
(Here we emphasize what? What tone?)

No concordados: la persona del pronombre no coincide con el sujeto:
· ¡No seas embustero!/¡No me seas embustero!
(Here we emphasize what? What tone?)

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Take "Se comió tres platos" as an example. Since "se" is "pronombre dativo", does "se" mean "to himself/herself"? "He/She ate three dishes to himself/herself". Am I correct?
If this is correct, it's very similar to verbo reflexivo.

Answer 1

When we speak about emphasizing I think that it is a bit subjective but I will do my best.

From my point of view:

Comió tres platos. / Se comió tres platos. (Transitiva)

The first one is simply plain: you inform that someone ate three dishes. The second one emphasizes that someone was able to eat thre dishes, thus trying to remark that he/she could manage to do it.

Fue en seguida. / Se fue en seguida. (Intransitiva)

The first one is telling that someone left quickly. The second is telling the same but is paying more attention to the fact that he/she made the decision of leaving.

¡No seas embustero!/¡No me seas embustero!

The first one is telling someone not to be a liar. The second one tells the same but it is also remarking that he/she (the speaker) does not want that he/she (the referred) tries to lie to me.

Update

Take "Se comió tres platos" as an example. Since "se" is "pronombre dativo", does "se" mean "to himself/herself"? "He/She ate three dishes to himself/herself". Am I correct? If this is correct, it's very similar to verbo reflexivo.

Be careful, "se" is a "prononmbre dativo" for emphasizing the action of the verb. The meaning in "se comió tres platos" is "he/she could manage to eat three dishes", it means that it was a lot of food and he/she did that.

Answer 2

To add to zirrus' answer:

Fue en seguida. / Se fue en seguida. (Intransitiva)

This form is quite used, and the change of emphasis is well defined. The first form, more plain , implies that he went somewhere (the place might be tacit, but it's asssumed to be known) ("He went at once "). The second form, with "se", disregards this aspect ("where did he go?") and focuses on the subject, to state that he left the place; it's to be translated rather as "He left at once".