As mentioned by others above, it is when you achieve LT or multiple Lifetime stati. I've done 4 airlines and one Hotel chain, so I did what I need to, I still have to chase/earn TK status every year (or two) but generally knowck that out in teh first few months. The funny thing (at least for some here) is that guess what? I still fly BA in most years enough to be earning Gold anyway, I still stay at Hilton';s enough to earn Diamond anyway, because I value the perks that they give me. I will not however take crazy routings or actively spend (essentially) more in order to fly/stay with them, I say "essentially" because I will spend an extra $50 a night or whatever to stay at a Hilton with a lounge when traveling with family, because they DO use the breakfast. I will spend a bit more for BA for the lounge, or to get my preferred seats, I will just not spend a crazy amount more. My relationship with DL is different, I am LT Gold, but Delta abandoned me years ago by cutting service totally to my main city, I would possibly be a Lifetime Diamond at this point had they done so, but I cannot imagine now ever getting beyond Lifetime Platinum.

This is all said through the prism of someone who has been doing this for decades, for someone starting out now, as a regular (rather than super) FT, is to pick the one that gives you real tangible benefits every time you fly, and just stick with that program.

Dr. J above, I fully concur, as while I may travel with carry on only 95% of the time, big family trips back and forth to/fr Europe and bringing items home, could often mean 8-12 bags, and the savings can be significant.

Addition to the above, as it is relevant to the subject.......What a difference 6 months makes! Due to the DL program changes, I actually am now Lifetime Platinum, and have started actively flying DL and partners even on less than optimal routes because I am not too far away from Lifetime Diamond....