I have completely dominated (semi-competitive) leagues by manipulating this in the last two years. One was a 6x6 roto, the other a 6x6 H2H. It makes your drafting decisions SO much easier at the tail end. My only worry is that this is starting to catch on with more casual players, so some of the RPs I'm looking for late are no longer there.
[sidenote]Admittedly, that 6th category really helps augment the non-starter strategy if it's an averaging category (like K/9), a negative category (like L or Hits), or a RP-counting category (like Holds).[/sidenote]
A standard 5x5 will be tougher to get the edge in when you're essentially "punting" Wins, but I think it can still work if you get the right number of guys and mix them well. Obviously you're getting a huge advantage in Saves, ERA, and WHIP, and can generally stay very competitive in Ks if you can keep your inning-count up.
I'm generally targeting 3 top- to middle-tier starters who have high K-rates to keep those innings up. I may bump this later in the season to 4 if a prospect is panning out and has some decent matchups (only if I'm falling way behind in Ks and need some innings eaten). After those 3 SPs, I'm generally drafting the best 4 closers I can get my hands on and then 3-4 setup guys with awesome ratios. Those setup guys generally go undrafted, and basically give you scalped saves instead of wins, and eat up 70 innings instead of the 150+ that a lower-tier SP would, at much better ratios.
By the end of the season, when everyone else with 5 SPs has used up 1300 IP, you'll be somewhere down around 1100-1150. You may only get to 65-70 wins on the season, leaving you towards the bottom of the pack, but 140+ Saves will guarantee you that spot and you'll definitely be at the top in ERA/WHIP.
The real key to this is being able to make daily moves. As long as you can get 8 pitchers with a chance to get innings everyday, you're okay. There's no way you can get away with leaving all your starters in there all the time and using only 4 RPs.
As for auction strategy... name all the Starters you can before you get into the RPs, and hopefully everybody will blow their wads on their 4th/5th starters before they get to their 3rd closers.
In a draft, I think this is a minor advantage. You'll be saving a couple picks in the 13-15th round and moving them down to 20+, but you'll also need to be drafting some higher quality starters and closers, meaning you're downgrading hitting a bit. The advantage really comes during the season with how you manage your pen. I don't think it necessarily gives you any better of a team than anybody else, and if there's others out there paying attention they're going to be able to pick up on something similar even later in the season. Managing your pitching staff and innings is really just a basic skill in any roto league, so it's not like this is ground-breaking by any means.