I'm confused by the two different sets of NPC rules in the DMG -- the templates on page 182-183, vs the Creating NPCs section on pages 186-188.
The templates aren't "NPC rules" at all. They're a shortcut intended to quickly help transform a monster into elite (or solo) versions. You don't start from scratch here, you start with an existing monster. Use these to create variation among your monsters.
The NPC rules, on the other hand, is a quick way of creating "monsters" that resemble player characters. That is, "monsters" that are mostly defined by their class, not their race (just like PCs). The main idea here is that you don't have to follow the full PC generation rules for NPCs. Treat these rules as officially endorsed shortcuts: you bend the rules, but end up with something reasonable anyway. And much quicker too. Use these for somewhat important allies and foes, which you expect to last longer than ten rounds of a single battle, and especially when the players will expect them to have signature class abilities.
Do note there are "NPC templates" too. Like any other template, these allow you to do a quick'n'dirty custom job on monsters. In this case, to give them a quick "class lookalike paint job" (in addition to making them elite). They're quick, but a bit crude. The full NPC rules give better results - if your goal is to mimic how a player character of a certain class ends up. If you only want elite Orcs with Fighter-y abilities, the NPC template will do fine.
Then there are the full class rules (used by PCs). As the DMG says, use this option sparingly, if at all. Creating a high-level character using the full rules will take a long time, and often the other options are perfectly adequate, and thus better.
Hope this clears everything up. Otherwise, ask again
