to understand preference settings

[afteryouwho]

Hi. Sorry to bother with this fundamental question but can't find an answer to what I want to know.
Is there somewhere that explains in detail the settings in "preferences"?
For instance:
If I leave a box unchecked, does that mean that the grayed-out default value is effective? I have set my upload speed to 68 which corresponds to about 75% of my upload speed and checked the box. The download speed is unchecked but indicates 100 grayed out. Does this mean that my download speed is unlimited or limited to 100 as a default? In some programs, 0 indicated unlimited.
Seems kinda basic but I can't find an explanation to this.
Thanks.

[afteryouwho]

Thanks for the speedy reply and the info.
It seems to be working fine so will just leave well enough alone!
Actually, I often get download speeds close to my 10 Mb service.