After a while, people (or even you) playing on your server will get bored of the official maps and will want custom maps. Almost everybody doesn't want to waste time downloading custom maps, but you can speed things up with the http resource downloading.
Installing a custom maps is an easy task. Usually you will download a zip file containing the custom map from a mapping site such as Counter-Map. But remember that depending of the author, the zip may either:
If you find yourself having a zip file of the first kind, you're lucky. You simply need to put this file into your mod folder and it should extract itself to the hirarchy.
In not, you simply need to copy the .BSP into the maps folder. Example: c:/HLserver/cstrike/maps/.
And that's it! Now you can make people download your maps faster with the Resource Downloading tweak.