Generally, when you start off, you want to rush GP10 as quick as possible but you also want at least one ward, preferably two, for gank protection. Just having a ward there will discourage enemy junglers from ganking your lane. Once you get GP10 (usually philo stone and heart of gold), that's when grabbing wards is of more priority than finishing your item build but you shouldn't need more than 5 wards per B.
For instance, with Sona I start off the mana regen part of philo stone, 4 wards, and 1 health pot. Most people go 3 wards and 2 health pot but I find the 4 ward start much more effective since I have sustain and the 4 wards guarantee me to stay in lane longer so that my first B to base I can get philo stone.