There are many examples of where a focus on equipment utilization can be more sustainable than other green ICT tactics. Here are some examples.

An October 2012 study from NDRC/WSP hammers on the utilization theme:

The single largest factor to increase the efficiency of typical server rooms is higher server utilization, for example through virtualization. Sharing servers across applications, and across customers in the case of cloud computing, can greatly increase average server utilization...
...the potential emissions savings from improving PUE may be less than what can be achieved from increasing server utilization or using cleaner electricity...
Replacing or “refreshing” outdated equipment saves energy by taking advantage of higher efficiency and lower idle power consumption in the newest equipment. However, the promise of more efficient hardware is not fully realized if server utilization levels are not increased as well. For example, an application using just 5% of an older server may run at 1% utilization on a newer one, not fully using the increased performance capabilities of the new hardware...
A private cloud, which consolidates servers and applications accessed across a company’s intranet, offers similar benefits and limitations to a public cloud. The main difference is potentially lower server utilization levels due to smaller economies of scale and diversity of users...
...if the servers are run at low utilization levels and/or powered by dirty electricity, colocation is only marginally better than an on-premise, non-virtualized server room when it comes to carbon emissions.

There are other green benefits implicit in these tactics. A more measured replacement policy - sweating our assets - can result in reduced equipment lifecycle impacts.

On the other hand, purchasing new gear can result in better utilization. A CIO recently told me, "[We] replaced hundreds of stand-alone printers and fax machines with energy efficient, cost effective multifunction devices. This allowed us to reduce costs through reduction in toner costs, reduced power consumption through fewer devices which were more energy efficient, reduced paper consumption by requiring duplex printing, and reduced landfill volume due to fewer devices being replaced."

Utilization can apply to storage and other aspects of ICT as well as to servers and printers.