When a reactor is "poisoned" with Xenon, the Xenon absorbs a large fraction of neutrons that otherwise would cause fission.
If you don't want to wait for the Xenon to decay you could construct a reactor that has a larger control swing than you would need otherwise -- for instance you could put in more and denser control rods. In that case, however, you need to have a lot of "excess reactivity" and also a lot of neutrons lost in the control rods under normal use, which in turn means the "neutron efficiency" is worse. (If you're not planning to breed Pu239 or U233 maybe you don't care)
Note the Xenon concentration can vary in different parts of the reactor so you have to manage the "oscillations" in space just as you do in time. Not a catastrophe, but definitely a hassle.
