With a pyrometer it is very easy to monitor the temperature development in the kiln and as such a pyrometer is strongly recommended. The alternative is that you judge/estimate the approximate temperature in the kiln on the basis the glow. In case of bisque firing where you want to maintain a temperature below 100 0C until your work is completely dry, this of coarse will not be possible.

But, like we explained in the raku firing procedure description, we always recommend to judge your glaze being matured or not with a torch rather than reading the pyrometer.
As such we cannot state here that you cannot do without a pyrometer. It is just very convenient.