GRDH vs. Multi-Look and Pixel Spacing vs. Resolution

Dear community,
for generating water masks from S1-Images I’m wondering whether it is mandatroy to apply Multi-Look to level GRDH -Data?
From my understanding level GRDH is already multi-looked?
As Pixel Sapcing and Resoultion differs, the final resolution which can be measured in GIS should have square dimensions, not rectangular. Is it therefor required to perform Multi-Look, to get GRDH-data in square dimensions?
Thanks for your help.

yes, GRD is already multi-looked. It is not a mandatory step, because before you can use SAR data in a GIS you have to geocode them which is done in SNAP during the Range Doppler Terrain Correction which also applies a resampling, resulting in square pixels anyway.

Multi-looking is good to make SLC data easier to handle but it makes little sense for GRD data unless you want to systematically alter the spatial resolution at consistent intervals.