Usually not that important, cause i dont tend to upgrade/change computer parts every year, usually bought whole new rig after bunch of years, with a single exception, when i swapped Athlon64 with its 939 board for C2D E8400, board and DDR2 RAM maybe like 2 years down the road? while keeping the rest of the rig.
That was a special situation though, i bought that A64 maybe half year before arrival of the first dual-core CPUs, which quickly became standard and the C2D came and made everything obsolete. I wanted to play Supreme Commander, early 2007 game, and it was literally no go on that single-core CPU, which was like year and half old at that time. Try imagining a game coming nowadays, which would be unplayable on 2015 CPU, something like Haswell or Broadwell. Ridiculous. On second thought, happy times :-D
TBH though, there is similar situation happening now, i bought my last rig a year ago, X99 with 6850k, and i would really love if it was possible to put in it one of the Skylake-X CPUs now and there was no need for a new board. Would be 400 EUROs cheaper, there would be no need to dismantle entire computer and i still am not sure about Windows 10 - i have OEM version and i am not very keen to buy a new license - again, pretty much my third W10 within a year. Hopefully there is a way to transfer it to the new board.