I find myself racking to secondary with virtually all of my brews after two weeks or so, so I am adding some risk to aerating or contaminating my beer. But I am also careful when I do perform these transfers, and to date, I have not run into these sort of issues.
Granted, I will leave a Kolsh or Blonde Ale alone in primary and these can be directly bottled or kegged. But even with my house pale ale or triple, I just find myself compeled to transfer. I suppose part of it is to remove the beer from the trub, cold break and floculated yeasts. Due to the frequency that I brew, I am not always on a "schedule" of when I will be able to bottle or keg at a specific time. I can have 10+ carboys fermenting at any given time.
I find personal satisfaction when I see the beer moved over to the secondary, in a carboy that doesn't have krausen spooge above the beer, or a ton of settlement on the bottom. For several years I have read that this step is not necessary, so am I just following directions that I learned over 15 years ago when I started? Probably. But odd to say, I enjoy doing this, getting the hydrometer reading and tasting to determine how the beer is coming along. If I see any airlock activity I wait to transfer, being careful not to transfer too sone.
Better brewers than I say it is ok to just leave your beer alone and just use one carboy, so if nothing I have said resonates, go for it.