Salut Grace, that means you'll get the fastest download your line allows, normally you should let that to 100%. For the upload, you benefit from lowering the bandwidth to 90% normally (lowering to 90% can help download speeds, lowering it more has no effect and damage the network).
Note that you shouldn't rely on the % of speed in LW but on the speed in KB/s which is far more precise depending on your connection. For exemple, my upload speed is 40KB/s, I lower it to 35KB/s so my download speeds aren't affected.
Note2: they sell you connections like that 1Mb/s down and 256Kb/s uploading. That means in LW terms 125KB/s (8kbps = 1KB/s) down and 32 KB/s upload.
Bonne chance
