Is there any merit to doing daily, very short runs before a half marathong?

As above,  does the idea of "Keeping the muscles ticking over" by a few small, slow runs hold any merit?

It depends on the individual to some extent, and over what period.

The one race I did where I hadn't run for a few days before the event, I felt sluggish and it took me a while to get into the run.  Since then I've always done a short run (3 to 5 miles) on the day before the event - this keeps the legs "ticking over" and also allows you to release some of the nervous energy prior to the event (without depleting your energy reserves).   

I just had a whole week off, ran a half today and PB'd again (same as the last time I raced a half, though I had 2 weeks off last time) - so for me I'm happy not to go for small ones to keep my muscles ticking over - I was aching to go out in the week though.  I may try a couple of miles the day or 2 before, next time.  I did a couple of laps of the track prior to the start though as it was bloody freezing, perhaps that's why I started fairly solidly rather than that hard first mile I usually have?