Should you? Yes. Population directly affects your income and your influence, and you want both of those numbers to be as high as possible.
When? Try to do it before the planet's population maxes out. The faster it grows, the better.

Up to a point.

For smaller planets, that point (for my playing style) is one Advanced Farm (10 mt of food production, giving the planet a total of 15mt). This size population can usually be kept happy with a single VR Center. A Stock Exchange also gives a small approval bonus.

If you want to grow a bit more without getting out of control, you'll have to micromanage building upgrades when you get new levels of farming. A population of 23 billion can be kept in line by about 4 VR Centers. This is with some bonuses for racial Morale ability, some trade goods like Ultra Spices, and maybe a Morale mining starbase. You can get to 23 billion population by building one advanced farm for 10mt and building another farm up to Intensive Farming for 8mt (which means stopping the upgrade to Advanced when you research that) plus the native 5mt for the planet. Fewer bonuses probably means adding 1 or two more VR Centers.

Once you hit 25 billion in population, you're in the approval toilet without a plunger. With racial bonuses maxed out, all relevant trade goods, and a Morale starbase, it will take at least 8 VR centers and sometimes as much as 10 to keep the planet's approval around 70 to 80% (depending on your tax rate). The good news is that once you pass 25, approval doesn't get any lower. Any population between 25 and 100 (the theoretical maximum, I've never gotten there) will have the same base approval rating.

Keep in mind that for a really high pop planet, you'll need at least 20 tiles' worth of VR Centers and Advanced Farms to make it worthwhile to pursue the max population. If you have room, may I suggest building your Econ capital and Political capital there, dismantle the starport, and if you still have factories left, build them over with Stock Exchanges.

Heh heh heh... or you could just mod the research buildings to make "genetically modified" food . Eg.

Lab level 1 - 1M food
Level 2 - 2M food
Level 3 - 3M food
Level 4 - 4-5M food
Invention Matrix and Discovery sphere can be something along the lines of 8 - 12M food.

The only drawback to this is that the lab buildings have a maintainance cost... But hey, you can build them on both the research bonus tiles and the food bonus tiles.

I consistantly dominate with minimal thought to high populations. On the times I bother at all I preplan what planet will be my breeding pit. Make it the one with the most Morale tiles. Put your economic and political capitals on it and fill up on Stock Exchanges. Economy starbases if you feel real frisky and your invasion breeding center is ready to roll. Pop out troop transports with 1 troop on them from your industry center and stack them outside the world. Siphon off troops to store for later use. Losing focus on your question. It all depends how you play.