People do this all the time. As I understand it, the reason why it's not recommended is that jets are "calibrated" by their diameter. If you ream the jet out (ie change the inside diameter) with that wire then you have altered the calibration of the jet and you can't put it back the way it was. On the other hand, if you don't ream the jet out with the wire, you may well leave a partially blocked jet that also won't be correctly calibrated. The recommended method is by soaking it in solvent and blowing it out with compressed air.
You need to find out the exact diameter that the jet or passageway is supposed to be and get something that size. Often a tiny drill of appropriate size is good.
If you go plunging around in there with the wrong size you may make scratches or affect the passageway/jet opening and never get it running correctly without replacing the damaged parts.