Like Dave says, it's not normally critical. Especially in relatively noise free environments
where you have a good strong IR signal.

But, if you need the absolute maximum range, under less than favorable conditions, then
it's a lot more important. If your carrier frequency is spot-on the center band-pass frequency
of the IR receiver, it's more likely to work under less than optimum conditions.

The IR receiver is more sensitive to the signal when it's spot-on the center band-pass
frequency.

Even little things like matching the wavelength of the IRLED to the IR receiver can make a
BIG difference if it has to work reliably under various conditions.