Any riders following you in an event will be less than pleased if you start weaving all over the place. If you can't ride up a climb without zig zagging then you need to hop off the bike and push up the climb at the side of the road out of the way of those who are still riding.
I often zig-zag on the fixed wheel bike to get up some climbs too!
I was just thinking of this example of when it's not really on myself, I saw someone fall off on Mow Cop too (And there's a picture of another faller in the report in CW too.) I think I might have seen the faller that stopped Kestevan, had a yellow frame, as I think I passed Kestevan a little later leaning against a stone wall eating a banana in a CC jersey (Kestevan, not the banana!).