Accounts with administrative privileges, and the programs that run under those accounts, have or can get access to all files in the system. If the user of that account accidentally causes malware to run, the malware can damage more under an administrative account than a standard account. Users under standard accounts can also be prevented from making changes that are harmful, dangerous, or out of standard. Most malware these days tries to move data over the Internet, which can affect network performance, if it isn't an antivirus scam.
However, from a security standpoint, you've already given it all away by allowing physical access (unless you have some specialized hardware), which you must do for the developers to do their job. The user can boot from a live CD or USB device and access any files on the hard drive, and then perform any operations over the network they want.
"Network" security should be taken care of by network security devices at least one step "inside" the edge, i.e. switches, ASA firewalls, etc. End devices can help with network security but shouldn't be totally responsible for it.
If you want the developers to be able to install software, they'll need admin rights. One possible thing that can be done is isolate developers on their own logical (or even physical) network, where if any trouble arises it cannot affect the rest of the company. If the developers are valuable enough to the company it might even be beneficial to give them their own Internet connection.