Has anyone ridden without the spring. I can't see what it does. Current pads are curved at the ends and this holds them in. The spring is very fiddly and I think it helps the pads to wear slightly  unevenly as I've had an issue with this.Maybe It's been in the wrong way round. Any help appreciated

Took it off mine. It helps keep the pads against the disc when going through deep mud or water so the bite point is more consistent. The downside is that the pads rub slightly on the disc. Last time I rode in the alps on the very long downhills the front brake kept overheating, this didn't happen with the old style caliper.

I think gas gas team riders take the spring off or run the old style caliper

There was a thread about this some time ago..Opinion was it's not needed.I took mine off because it made the brake drag slightly,now its fine,no downside to not having it

Thanks for the replies so far. I think the "tails" of the spring force the pads apart and therefore the pistons to a small extent at one end at least. This affects braking I feel. Would love to know how it's supposed to work though.

The spring helps the pad apply and retract correctly. If you run without them and find your pads wear unevenly or if your leever has long / soft travel at first brake application for some time put them back in. Generally trials and mx bikes are OK without the springs, road bikes and cars are not. The larger the brake pad and higher wheel rpm the more important the spring.

Had no problem leaving mine in.