Many people have mentioned different status benefits on different airlines and this is very true. I have miles in many programs I would never dream of earning status. I earn miles in about 20 programs but credit all flown miles to 5 or 6 programs where I intend to retain status this year. As for the benefits of status on the different programs, they are unique. For example, my case:

1) AA EXP - unlimited domestic upgrades with 90% clearance, 8 system-wides good from dirt cheap international fares, 100% mileage bonus throughout Oneworld
2) BA Gold - first class and business class lounge access alliance wide - including the ORD/LAX/MIA/JFK AA F lounges when flying domestically on AA - One-way awards, and the ability to upgrade from WT+ to a superior J product for only 25K miles RT
3) UA 1K - E+ system-wide, domestic upgrades when flying coach, 6 system-wides for international
4) BMI Gold - 4 free upgrades to premium econ (soon similar seat to UA J) ORD-MAN, lounge access alliance wide including UA/US domestic, bonus miles throughout the alliance unlike UA, and the ability to earn 6.25% of miles flown when paying F over a certain threshold
5) CO PLT - CO/NW domestic upgrades, free Pres Club so CO/DL/NW/AS/KL lounge access, Skyteam lounge, baggage, and priority benies, 125% mileage bonus throughout Skyteam
6) AS MVPG - Domestic upgrades when flying AS, a variety of partners to earn and burn on, one-way domestic awards for 10K miles. (Lounge access already covered by CO Pres).

But the OP referenced a thread that just talks about where you have miles. While the above are my primary status airlines, I earn in about 10 other programs though I would never credit EQM to them. Why? Because of unique earning opportunities.

For example, if I rent a car next month, there is only one program I will consider: CO, for the current 5K bonus I can receive as a travel Club member.

But when converting SPG points to miles, there is only one program I will consider (absent any limitted time promo): Asia Miles, for their 60K mile award on BA in business class to europe (from eastern/central US only).

When redeeming intra-Africa on KQ, all of a sudden I need NW miles. Other programs charge 2.5X for the same award. So when NW has a special partner bonus going on, I may as well credit some hotel, car, etc activity to them.