An expression pedal with its own switch in the "toe down" position can be programmed to act just like a real wah-wah pedal, in addition to other creative control moves depending on your needs. Generally speaking, for live performance, you want your footpedal moves to be compact and efficient in terms of the number of moves you make and the distance your feet travel in order to initiate these moves...or...before you know it, you look like you're doing the riverdance.
Personally speaking, on a preset-by-preset basis, I want as MUCH control as I can possibly get available to me at all times, especially for complex soundscapes where trailer echo/reverb and more subtle "blended" tones are required. In this case, footswitching is just too abrubt. I use the Behringer FCB1010, which has 2 expression pedals, and I also utilize a 3rd exp pedal plugged directly into the AxeFx. I wouldn't have it any other way as it allows me a TON of tonal flexibility and balance between different effects...but that 's just how I like it. I think everyone should set their pedals up in a way that makes sense for the way he/she prefers.
