Common problems encountered when dealing with spatially extended syste
ms in extensive chaos regimes are discussed from the point of view of
the experimentalist. It is argued that both local and global probes ar
e insufficient and potentially misleading, and that the space-time evo
lution of at least one variable - even with low local resolution - sho
uld be accessible in order to estimate the possibly large-scale cohere
nce in spatiotemporal chaos regimes.