Hello,
Each "get log" request is a fairly light-weight request through the device's SOMA interface. This is an XML over HTTPS request; the size of the response is relatively small.
It would create some load on the device; it's hard to say what would be the impact without some measurements. You can try to monitor CPU and system utilization while you're running dp:tailLog.
Enabling debug logging would have a different and probably more substantial effect. Unlike debug logging, "dp:tailLog" does not write anything to the disk on the device so it would probably be less noticeable.
Regards,
-Alexander