IMPORTANCE:
In all fields that deal with geology - the concept of geological time scale is paramount.
This also includes environmental management.
For example, in an area, contaminants are seeping (migrating) 5 cm/ yr or 5 mm/ yr.
The migration of these contaminants does not mean much in 10–20 years time scale.
However, this migration becomes significant in geological time scales, say 20,000 years. What if this contaminant was radioactive waste.
To put in layman terms, processes in environments management which may be insignificant in decade scale become significant in geological time scale
SHORTCOMINGS:
A possible weakness is that the chunks of time represented are gigantic. More detailed versions of the general time scale would depict ~ 4.6 billion years of events; they would take up a lot of space. A chart chronicling the geologic history of Earth could stretch for several city blocks.
Also Timescale for us as human beings is the difficulty to comprehend the actual timescales we are dealing with. The Geologic Timescale is dealing with Epochs, Eras, Eons. As human beings we live our lives within a century (if we are lucky). Naturally we understand seconds, minutes, hours, days and years in a direct and personal way. These units are the timescale we live our lives through.