If you have one such installation, then you really do not care about the "accuracy" of the time.  However if you have multiple such installations then you want them all to have the same time (if you will be comparing logs between them, for example).  At some point it becomes "cheaper" to spend thousands of dollars per site to have a single Stratum 0 timesource (for example, the GPS system) at each site (and thus comparable time stamps) than it is to pay someone to go though the rigamarole of computing offsets and slew rates between sites to be able to do accurate comparison.  And if you communicate any of that info to outsiders then being able to say "my log timestamps are accurate to +/- 10 nanoseconds so it must be you who is farked up" (and be able to prove it) has immense value.