Skipping necessary quests

[cabby]

It was a promo video, of course it's main goal is to sell the guides.

[mzanker]

I haven't really had any problems with SIS up to level 60 - it pretty much does what it says on the tin. I dug out an old level 22 draenei priest, did a faction transfer to horde, then let SIS do its stuff - it quickly caught up with me. Sure, there were a few quests far below my level but I assumed they were important parts of quest chains.

I think things get a bit more difficult when you hit Outland. There is a lot of rep dependency and, following advice here, I turned off SIS (by setting to 80). This worked great - I was still getting good XP from quests and dinged 70 just as I was finishing Nagrand (admittedly with some help from healing instances).

Now level 75 and on the level 73 part of the guide - still getting good XP, mobs are easy to kill, and once I ding 80 I reckon I'll still have a few levels left in the guide to get some easy rep/gold.

TL;DR - SIS is fine up to level 60 - best to disable it for Outland and Northrend.