When I install the NetworkManager application, dhcpcd is removed and replaced by dhclient. I've configured a network interface (eth0) with DHCP (for IP, DNS, NIS, NTP). 
When I use dhcpcd it waits for some seconds after sending the DHCP request. In this wait period /etc/resolv.conf and the configuration files for the other services are modified with the data received from the DHCP server.
When I use dhclient, there is no wait period so the boot process resumes right after sending the DHCP request. But it takes some time to receive the data from the DHCP server and to modify the configuration files for the network services. For me this has the consequence that mounting of NFS shares, which is performed right after starting the DHCP client process, fails due to false network configuration.
I think that there should be a wait period after startup of the DHCP client when using dhclient to give the system some time to modify the configuration files.