To sponge, or not to sponge ...

Hi everyone,

just a quick question to see what you all thinkabout using a sponge.  I've been searching for a more sour flavour, and have just started using the sponge method...

I mix the starter (100% hydration) with half the flour and all the water and let it sit for a few hours (around 4-5 depending what I'm doing) then add the rest of the flour and the salt, and mix.  Leave for a couple of hours or so (again, depending) fold once, then leave again for another couple of hours, then fold again and shape very gently.  Leave for 15 mins, then shape again and put into proving basket.  Leave for around 2 hours, then bake. 

Previously, I'd miss out the sponge bit, and just mix everything as before, leaving it to prove overnight in the fridge before baking in the morning.

I realise there are quite a few changes here, but what do you guys think:?  Is there a definite purpose behind using the sponge method?  It gets really bubbly after a couple of hours, and my husband and I both noticed a better flavour.

Any thoughts?

Thank you!