Well basically I want to use one of my MacBook Pros as a desktop to share my printer, scanner, address books and ftp between my other laptops. I won't be doing any intensive stuff...
Basically I wanted to know if I will have to compromise anything by switching from a client to a server?
Ya know, this is a very valid question... however, to solve your needs:
1 - Printer sharing is available in Snow Leopard (and previous) versions. Enable sharing on whatever computer the printer is installed on, then install remote printers on your other machines.
2 - I don't know what kind of scanner you have, however, if it's part of an all-in-one printer unit, you *may* be able to share it on the network.
3 - Your address book will automatically sync if you are using the mobile.me service.
4 - Instead of FTP, you'd be better off using file sharing on your network, or by using mobile.me's iDisk. With iDisk, if your files aren't beyond the storage allowance, it's a nice thing to use because you can access your files from any internet enabled machine.
To give you an idea about the difference between server & client editions, many people I know put their servers in a closet and forget they're there (assuming they're running stable). They're not designed for use as a desktop machine. They'd be great if you were hosting websites, ingoing and outgoing email servers, and other services where you'd be handling large amounts of data.
Hope this helps. Everyone here mentions really great stuff, and it's very difficult to wrap your head around at first - but keep digging, it's interesting stuff!