Since you're talking about insertion, I assume you're now referring to /iline and not to /aline. If so, logging is undesirable exactly because /iline can insert lines; to insert a line in the middle of a log file, mirc has to rewrite the entire file below that line. Now imagine calling /iline in a loop when the log file has grown considerably big... Doing a /savebuf yourself after the loop has finished is indeed a far better approach.
In my opinion, /*line commands should not log by default. That said, a new /*line switch that makes the command update the log file might be of use (or abuse :tongue:) to some.