Some have a good idea, some don't. But if you do, then you can knock out several options right away. If you are actively looking for a different job and are looking to refinance, you obviously don't want to lock yourself into long term security when you know you're probably not going to use it. If your neighborhood is appreciating by leaps and bounds and you think you'll want to tap that equity a year or two from now for whatever reason, you also don't want to pay a higher interest rate for a longer fixed term when a cash-out refinance in the near future will turn that security into wasted money. In that case, it can make a lot of sense to think about the fact that the average life of a mortgage is only seven years.
Many people refinance before that time.
If you end up staying in the home, you've got what you want and if you don't, then you've kept your payment as low as possible for the time you spent in the home. Some people object to the idea of refinancing more than once, but the likelihood is that you'll end up doing it anyway. Finally, a note about margins and indices. Many people get needlessly wrapped up in these things. Since we talked about the fact that most people refinance when the fixed term is completed anyway, it really doesn't make a lot of sense to worry about this.