bright objects, with saturation limits of $K\approx 4-6$. However, MIRI MRS is composed of four integral field units (IFUs) of different wavelength ranges, each of which is split into three sub-channels, which must be imaged individually. Thus, MIRI requires three visits for complete wavelength coverage. MIRI MRS also faces unique challenges, including lower-than-expected efficiency and more complicated systematics than the other modes [@2015PASP..127..686G].

All of the other spectroscopic observing modes for the four instruments require one visit each. As designed, JWST does not have parallel observation capability. The telescope hardware will allow it, and studies are being done to implement this capability [@2014PASP..126.1134B], but this does not allow multiple observations of the same target at the same time. One proposal to implement truly simultaneous observations of the same target, due to @2017PASP..129a5001S, would involve adding an additional, short-wavelength spectroscopy channel to NIRCam.

The different observing modes are useful for different types of observations. For example, the only instruments that can take high resolution (R$\gtrsim$1500) spectra are NIRSpec in its high-resolution modes and MIRI MRS. The rest of the modes are relatively similar to each other in functionality, except for the NIRSpec Prism and MIRI LRS, both of which are low 