From the spiritual point of view with wife has the same effect on consciousness as with someone else, as far as the act itself is concerned. Of course with one’s wife or a single person whom one loves, there is already an intermingling of consciousness. But having more partners creates chaos in the system somewhat like taking all kinds of things of different people for you to sort out inside your being, and giving your precious pearls to them and losing them eventually.
With wife or single partner this risk is minimized since one grows one being within.
Is it an obstacle in sadhana?
Well, yes because sex creates lot of vital excitement and after the act the consciousness takes a dip into dense dark fields exposing and making one vulnerable to forces of darkness and falsehood. The energy that one throws out in sexual act is the same energy that, if conserved and sublimated upwards feeds the aspiration and is eventually transmuted into higher forms of inner energy, viz a viz retas (fluid) to tejas (heat or vital force) to vidyut (electrical or mental illumination) and viryas (spiritual strength and power). It is not about right and wrong or any moral issues but about wasting the vital-physical energy into extreme pleasure or turning it upwards into spiritual knowledge and power.
Having said that it is understood that sexual mastery does not come easily. Its roots are in the very body and much before even animal life began. One has to be patient and apply sanyama (self regulation) followed eventually by nigraha (complete control). One should not make it the centre of conflict within. A
Affectionately,
Alok Da