When I bought my bike it came with a spare set of chain and sprockets, which was nice I thought.

Now I've looked into it a little I've realised that the front is 1 tooth down and rear is 1 tooth larger.
Firstly I realise how gearing changes affect things, and that the -1 on the front will have much more of an effect than the +1 tooth rear.

Easiest thing for me to do would be to just swap out the front.
Any negative effects from going down 1 tooth on the front - does the chain start eating the sliders for example?
I appreciate there will be a larger gap between the sprocket and the case saver afterwards but I'm not too bothered about that.

Finally, is it worth doing?

-1 on the front is almost +3 on the rear, so that's a big change from standard. It must be a wheelie monster!

The good thing is sprockets are cheap and easy to change.

Back in the day everyone who owned a 990 went one down on the front. I think it was to a 16 tooth (but can't be sure)

It was just accepted that this offered a better balance for rapid acceleration and top end speed. I'm still running a 16 tooth front but with a standard back.