Network Time Synchronization is important: every aspect of maintaining an IT or security surveillance network requires accurate knowledge of when events have happened. If you were to assume that the little clock on the bottom right hand corner of your screen was inherently accurate you would be sadly disappointed. Many clocks which support network devices, IT servers or workstations are rarely checked after an initial manual setup, and backed-up by a battery-based, clock-calendar programme that has no capacity for negating time drift which can sometimes amount to 1 second per day and perhaps minutes, or hours, over longer periods. Considering that DVR and NVR systems should run unattended for months, or years, to allow this to happen in an environment where the veracity of evidential data requires accurate time-stamping is not appropriate.
Trying to accurately match time logs between IP devices on a network without synchronised time is a challenge, perhaps impossible, as this is the only frame of reference between all IP devices. Implications exist when time is mis-matched: financial services may be legally required to demonstrate accurate timekeeping; security breaches and CCTV data must match timestamps to be effective. Within a closed network, such as CCTV, it is not practical to synchronise your NTP using a public Internet Time Server because a permanently open port leaves the network open to cyber-attack. You must also consider if the provider of that ITP has any guarantee of service or accuracy.