Give them the liberty to choose!
Give them the liberty to choose!
Let's also not forget that when developers are choosing their own machines, they're doing so on company time. It's certainly not cost effective to have developers doing comparison shopping on machines. And it's absolutely not cost effective to have developers putting together their own machines from parts (as some would happily do if allowed).
Additionally, it would be frustrating to use your credits too soon and then the guy next to you gets something twice as good one month later. So just play it safe by keeping everyone on the same playing field.
However, I'm sure the tax benefit is small compared to the potential for increased productivity and output. But try explaining that to the average CFO.
It implies that every developer is responsible for his/her own workstation maintenance, though, and that might be a risk/pain you don't want.