Why would I want to pre-heat a pan before cooking?
That really depends on what you want to make! For example, the Spanish Omelette (potatos, onions, eggs, &quot;potato omelette&quot;) needs to be poured in a pan which has had to be preheating for some time until it's quite hot (you can pour a little bit of olive oil, and if you move it and it moves VERY fast, that's usually a sign. Don't overdue it as you can &quot;burn&quot; the oil!). That is so you can &quot;sear&quot; the outside while the inside still remains with the liquids and flavours!
If you want to sear a meat (I asked a question about that a little ago, or in the case of the omelette, cook it on the outside so it can have a shape, and let the omelette be runny on the inside. Here you can see something I made the other day!

Another example in which I use it, if I'm cooking curry or something related with CHICKEN, I'd just toast a bit (in Spanish we call it &quot;to golden the chicken&quot;, &quot;dorar el pollo&quot;), which basically is at high heat (PRE-HEATED!!) and with some olive oil, cook it quickly, so the outside is seared, but it still has all the liquids on the inside (still raw in most cases because of this quick cooking), and you can add it later!