Energy Efficiency in BBP
Pokemon battling is just as intense as any other sport -- even for a highly-trained Pokemon, fighting can be both physically and mentally exhausting. On cartridge, this exhaustion is represented through a move's PP, but in Smogon Battle-By-Post we instead use a resource called Energy (or EN for short). A Pokemon will always start each battle with 100 EN. Attacking consumes varying amounts of EN depending on the strength of the attack (more powerful attacks are generally associated with high EN costs). If a Pokemon runs out of EN it faints of exhaustion. There are also factors that can increase or decrease the Energy cost of a move; for example, repeating the same attack over and over will cost massive amounts of EN, while using a move that matches the Type of your Pokemon costs slightly less.
Because repeating attacks consecutively will quickly wear out your Pokemon, a common strategy is to alternate between your two most useful attacks in battle. For example, let's say you determine that your Pokemon's strongest attack is Dark Pulse and its second strongest is Night Slash. If you were to just order Dark Pulse three times in a row, it would consume 30 EN in total (or 27 for a Dark-Type Pokemon). If you instead choose to order Dark Pulse, then Shadow Ball, then Dark Pulse again, you would only consume 17 EN (14 EN for a Dark-Type). The reduction in damage output from using this strategy is generally very small, but the difference in EN cost certainly isn't! Use this strategy of alternating attacks and you'll definitely see an improvement in your Pokemon's performance.
Of course, it's always a great happenstance when your opponent's Pokemon runs out of energy. Once your team starts falling behind on HP, sometimes all you can do is hope to knock out your opponent through sheer exhaustion. The most obvious way to achieve this is by stalling out your opponent, but you can also speed up the process by using Pressure or Spite to increase the EN cost of the opponent's moves. After that, make sure the opponent's Pokemon doesn't get an opportunity to chill by using a move like Taunt or Encore to rile it up. Even if you don't manage to score a complete KO, leaving your opponent with very little EN will force them to rely on weak, low-cost moves until they get the chance to Chill and regain their EN.
Typically the damage moves deal exceeds their Energy costs by a wide margin, so don't expect to see Pokemon run out of Energy very often. It usually only happens when either: the match drags on exceptionally long, or a player accidentally ordered their Pokemon to use a lot of high-cost attacks without thinking. In either case, do your best to make sure you're the one who comes out on top in these kinds of situations!