IMO, once you actually experience how the batch comes out with a long primary, you're sold on it.
I have two bigger brews planned that will be going 6-8 weeks on the yeast, maybe longer. I plan to age them on oak for another 3-6 weeks (depends on if I use cubes or spirals), if not longer. I just hope to have a couple of 6+ gallon sanke kegs to use as primaries for these batches. That, right there, eliminates any concerns someone should have when looking at longer primary stages.
Personally, I'm not racking off the yeast just to get the brew to clear (the major reason people give for getting off of it after 1-2 weeks)... IME, I'm getting VERY clear brews with long primaries. I'm also racking less often, so the batch has less exposure to air/oxygen (when it's bad for it). I'm only racking to another vessel, these days, when I'm aging on a flavor element that either works better/best when NOT on the yeast. Or, when I need to get it off of a flavor element/addition before adding another one to the brew. I'll be researching, as I get closer to the time to oak, if I will actually have any benefit from racking out of primary before adding the oak for the bigger brews. I could be better off just leaving the brew in primary, adding the oak when it's time, for however long, then bottling it up.