Shukra Puja is to appease the planet Venus. It is very useful & beneficial puja, since it's worship strengthens benefic Venus & increases its positive influence and pacifies malefic effects of the planet & neutralizes its negative effect. Venus Puja is recommended for those having malefic Venus or wrongly placed Venus as per horoscope.
Venus is the best benefic at the material level. It instils grace, tenderness and beauty into the yogas that it participates in. Its affliction is generally adverse for marital harmony or normal sex life.
The planets are to propitiated against their evil influences, to ward off them, the Venus Puja is done with faith to ward off all evils of Venus as per the horoscope.