1 tooth change in the front sprocket is like 3 in the back.
Folks rarely change the front unless doing desert high speed riding.
supercross bikes typically have 3 additional teeth added to give the bike boost out of corners and they typically never reach top end due to the tight quick turns so loss on top is not such a big deal for them.
Motocross typically on a 250 two stroke or 450 four stroke 1 tooth is enough to give a tad bid extra boost/acceleration out of corners and help the engine rev faster.
The extra tooth will reduce top end sooner, not be much but it is noticable. You will find you will have to shift sooner than you did with the original sprocket.
In the 10yrs I have been riding, 1 tooth has been just right on bikes that I wanted extra boost out of corners.
The only time I would add two teeth if it wasn;t for supercross would possibley be for trail riding. I did this on my wife's 125 to give it extra boost on the bottom since she does not rev the bike too high. I heard of some folks doing on a 250F's but I wouldn't due to having to shift too soon for my liking.
Spokes574