The summer is over, so the annual political party season has ground around again. And with it come the same questions that have been ducked for years - why on earth do they bother and does anybody really care?

For the best part of a month every autumn, just as the nights start to draw in and the bone-soddening drizzle descends, the political equivalent of SAD (Seasonal Affective Disorder) gets under way.

Virtually all normal political business, even much government activity, is put on hold as the parties gear up for what they still like to pretend are defining rallies, in various locations around the UK.

It used to be the seaside; Blackpool, Brighton and Bournemouth but nowadays it's more likely to be Glasgow, Manchester and Birmingham.

The reason for the switch away from traditional holiday venues speaks volumes about the way these events have been transformed from well-attended party gatherings with a huge social and fun element, to hard-headed, money-making enterprises more akin to trade shows. Pleasure beaches and disco nights have long gone, replaced by lobbyist-led receptions and utterly pointless fringe meetings.

The media circus dutifully turns out in force, although in smaller and smaller numbers and with less and less enthusiasm, just like the delegates.

Cavernous halls have been either abandoned or re-designed to make them look fuller than they really are and the exhibition areas are all packed with the same corporate stalls, peddling their wares with scant regard to the political nature of the events.

The demise of the conferences can be traced back to the rise of party control and the homogenisation of politics. The control was always there to an extent, and the Conservatives, in particular, never made any bones about the fact that conference debates - no votes here - did not inform policy. The attendees are not even delegates but representatives. But as they were often the party in government, the conferences at least gave them a platform to make genuine announcements about things that would really happen.

There is still a bit of that, but do the ruling party really need a week away from London to do it, other than to show they are "in touch" with the provinces?

As for the other parties, there is even less reason to bother.

Labour long ago decided they couldn't continue with union block votes dominating their rallies and setting party policy. "All those in favour of scrapping Britain's defences - 17 million for [thank you comrades from the Metal Bashers Union] and 24 against [thank you the shadow cabinet]".

So the block vote has gone and, in any case, leaders will now openly declare that, not only will such "unhelpful" motions not become manifesto promises if they do miraculously make it past the Conference Arrangements Committee, they will in fact be ignored completely and with some enthusiasm.

The Liberal Democrats have always prided themselves on being different. "Conference Rules!", they say, and still seem to believe it. Motions on legalising glue sniffing or banning the use of leather can be passed until the fully-protected cows come home.

The media will have great fun with them, but that will be the last anyone hears of these "policies".

The demise of ideology-based politics has contributed to this sense of pointlessness as all three major parties scramble into the middle ground in the belief that is where elections are won and lost. It may be true but, as Margaret Thatcher proved, it is quite possible to radically shift the centre ground, not just inch it a little to the left or right, and conferences might be a good place to start that argument. But it won't happen.

So what is left? The leaders, that's what. Opinion polls before the events will show who is up and down and the leaders will have spent the long summer agonising over their big speeches and how they can use them to sway those poll ratings, delight their party faithful and prove they should be running the country.

Their speeches are the big events, the only events that matter, and they will indeed sway the opinion polls. Traditionally, leaders get a poll bounce after their speeches, which may have far more to do with the dutiful, licence-fee supporting TV coverage than anything else. Even though much of it goes unwatched, it is still hard to ignore.

But two weeks after the event, the relative poll positions will fall back to roughly where they were before the conferences and, come November, it will be hard to remember more than the odd soundbite.

Just as much could have been achieved with a weekend seminar in a London hotel.