A little extra time on the primary fermenter's yeast helps clean up off flavors. When I was first brewing, the steadfast rule was a week in primary, two in a secondary and three in bottles. A lot of my beers do better with ten or more days in the primary.
Gravity, style, fermentation temperature and packaging method are all considerations.
Mind sharing those details and/or your recipe/kit/ingredients?
Secondary isn't totally necessary. I ferment three weeks in my primarys, then two weeks warm bottle condition, and 2 weeks in the fridge. My beers are super clear, and I don't notice any off-flavors. Let your brew sit and ferment away. The yeast have a lot of work to do, so let them do it.
If you're going to secondary (some do, some don't. There is plenty of debate on that issue), keep an eye on your airlock. When the bubbling stops, or slows down significantly, take hydrometer readings. When your reading stays the same for three days, then fermentation is complete.