Its all about getting the status, and the bonus points.

In my current job, I travel a lot.  I typically fly out every Sunday, and then back every Thursday.  That's 2 segments to the client, a rental car, 4 nights at a hotel, then 2 segments home.  I've become very methodical in my routine and it comforts me.  Would I rather be with my wife and kids?  Definitely, but the job pays well, and I get bonus points for flying, renting and lodging.  These bonuses help me have vacations inexpensively, they help me get on earlier flights (due to "status", a topic for another day) and help the mediocrity of it all seem a little more bearable.

I fly Delta, and I like them.  Most of my future posts about flying will discuss them because they are the airline I fly.  On my current client, I could fly Southwest direct (no layover) but I choose to do multiple segments because they help me reach status.  The statuses on Delta include:

1. Silver.  Puts you in zone 1 (you get on the plane after the pre-boards, 1st class, and sky priority).  You get on the upgrade list but forget about getting upgraded to first unless its a very rare day.  It takes 30 segments, or 7.5 weeks of travel assuming 4 segments per week.
2. Gold.  Gets you to Sky priority and lets you board after first.  This is the minimum that I like to get, as I can get on and get my large bag in the overhead where it is convenient to reach.  Nothing worse than having to go back 4 rows to get your bag against a sea of travellers when you have a tight connection.  This takes 60 segments, or 15 weeks of travel.  You may get bumped up 2 to 3 times in a year with Gold.
3. Platinum..  Still sky priority like Gold, but you will get much better service in terms of upgrades, as well as improved chance of getting to the top of the standby list when you need to take an earlier flight.  This takes 100 segments, or 25 weeks of travel.  I'm currently Platinum, and I get upgraded on about half my flights.
4. Diamond.  I've never been Diamond, though I hope to reach it in 2014.  It takes 140 segments or 35 weeks of travel (4 legs per week).  This increases your chance to get upgraded, and you get a free membership into the Sky Lounge.  Very nice.  You can travel 3 out of 4 weeks and still make this status by the end of the year.

Note, that you can also reach those statuses by miles instead of segments, but all of my flights are short hops, so I don't bother.  Also starting in 2014 there will be a dollar spent requirement as well that are called "MQDs".  More on that later.