A bigger sprocket (more teeth) on the rear wheel will make the bike quicker off the mark and accelerate better. This will have the effect of reducing the absolute top speed in top gear - but often this theoretical top speed is not achievable anyway.
A smaller front (gearbox) sprocket will have the same effect as above.
A bigger front sprocket / smaller rear sprocket will have the oppsite effect - slower off the mark but a better top speed. This is not normally recommended on sports bikes - it's more for small bikes (I did it to my old DT 175 MX) or for touring bikes to reduce the revs when in top to make things a bit more relaxed. If you change too radically in this direction you can make pulling away really difficult - if not impossible as the gearing will be too high.
The thing that is actually important is the final drive ratio itself. This begins to get mathematical but if you raise the ratio, say from 3.0:1 to 3.5:1 (Rear:Front), then you will get better acceleration and a lower top speed. And vice verca.
The reason I have explained this is because a single tooth change on the front has the same effect as 3 or 4 tooth change on the rear. If you do the maths you'll see what I mean.
I have been told that reducing the size of a front sprocket can cause excessive chain wear on some bikes. I've never done it this way so I can't comment.
Changing the rear sprocket for a larger one may give you problems with chain length - it may be too short to go around the bigger sprocket, esp if you are going up about 3 teeth or more and the chain is fairly unworn.
My latest experience was changing from a 43 tooth rear to a 46 on the Triumph. This had the effect of making the bike quicker but not as fast. An indicated 140mph is enough for me anyway. However, the most unexpected thing was that the bike was much easier to ride round town (which most of us have to do on occasion) as before 30-40mph sat uncomfortably between two gears. Now I can pootle around in third and I'm less stressed when the open road appears.
The most useful features of fiddling with sprocket sizes are:
you can easily do it yourself
it's (relatively) cheap
it's easy to undo it of you don't like it.
Man, this has become an essay. Hope this explains some of it.