Can you delete .log files?

[FOBSIDE]

I have a friend, who has some log files that are ridiculously large in file size. Can he just delete them or just delete the contents of them if he doesn't care/know what they mean? I'm specifically talking about the following files:

/WINNT/SYSTEM32/SVCHOST.LOG
/WINNT/SYSTEM32/NTSYS.LOG
/WINNT/SYSTEM32/SVCHOST.LOG.2003-W18

Thanks for any help.