I almost always brew with liquid yeast. I like the variety that comes in liquid form. I also like that the yeast is shipped in live culture. There are over 100 billion cells in your average smack pack. That's good for a beer with an original gravity of about 1.040. The manufacturers instructions say some single smack packs can tolerate up to 1.060, but I aim for a fermentation range where my co-workers are simply happy and not stressed in the least. So, unless I am making a super-low gravity beer, I always make a starter for my yeast. I follow the advice that is in John Palmer's book How To Brew:
1 pint of water
1/2 cup of dry malt extract
Boil the water and DME for 15 minutes, chill to 65 degrees, and transfer to a sanitized flask, pitch yeast, cover with a piece of sanitized aluminum foil, and wait 2-3 days.
I use a stir plate to propagate yeast. I swear by my stir plate.
Sure, it seems like just another piece of equipment that we homebrewers collect. Erlenmeyer flasks, carboys, racking cane, wine thief, tubing, to the non-brewer our brew spaces can straight up look like an episode of Breaking Bad. My stir plate was a wise investment. While I purchased mine you can actually make your own. It can be as simple as sourcing supplies and assembling parts but for as a homebrewer juggling work and life and brewing, I'm not so great with the DIY so I didn't go the make-my-own route. I'm sure I would have eventually figured out how but, the time it would have taken me and the frustration it would have given me were reasons enough for me to decide that my time was better spent brewing or devoting it to recipe formulation.
My stir plate and flask were roughly the cost of the ingredients for a high gravity beer using all Maris Otter and specialty grains.
Before I did starters, my lag time would vary and my beer didn't taste exactly how I envisioned it. Once I developed the habit of making a starter, my beers were noticeably better. Prior to that when brewing a high gravity beer, I would sometimes pitch 2 packs of yeast. Even that wasn't as effective as making a starter and using a stir plate. Once I stopped stressing out my yeast with a 1.080 wort they were happier and produced fewer off-flavors. And as a bonus, as the amount of DME used was not as much as a 2nd smack pack, I was saving on the cost of the extra smack pack. The stir plate paid back its investment in 10 batches. Good looking out stir plate, good looking out.