I almost never preinflate. The only time I really consider it is if I'm launching way overpowered or if the launch site is really sketchy and there's no room for error and even then I maybe take 30 seconds to do it. If you are slow and have the wing tip weighed down with enough sand, you can slowly inflate it during launch. If you're kite leaves the ground before you are ready, then you need to weight it down more next time.
The secret to a good quick, controlled launch is having the trim set for full power, and launch the kite with the bar sheeted fully in. This will inflate the foil the fastest and still give you good control. Of course on higher wind launches, be ready to pull the depower once it's pretty well inflated, takes a couple practices to get it right. I do this even with my Soul 15m on 20+ kt days. The Soul does take a little longer to inflate the wing tips compared to say a Sonic 2 just because there's more space.
I use a foil board so not launching big kites in strong wind. I never bother to pre inflate anymore, I lay the kite directly down wind and get all the lines untangled, slowly launch the kite and use plenty of bar pressure to inflate the tips. The Soul is super easy to inflate so you can do whatever you want. With the Sonic 2 or Sonic Race, I would only launch directly down wind. If you launch off to a side, the tip can lift up and go over too far and you have a mess. I get the side launch idea, reasonable idea but is not practical. When you are laying out the kite and making sure the lines are not tangled, by pulling on the front lines the front of the kite will take shape due to the fishing line that is in the kite. If you have an older kite without this, a little pre inflation helps.