I find that there are so many things seem selected, not sure if it is selected but they have 'M' as indicator. And those things do not exist in my computer, like scsi devices etc. So can I exclude them even they are default selected? Any advantages that remove those things and is there any disadvantages?

If you can provide a resource about this topic will be appriciated.

Thank you.

Those things with a M are loaded as modules. That's done by default to help detect a lot of common hardware. If you don't have the device in your computer, just select N and leave it out. There are many resources. If you want to read some specifics about each line in the kernel configuration, start by reading this file /usr/src/linux-2.4.22/Documentation/Configure.help if you have the default bare.i Slack kernel installed.

The advantage to removing them is that you will have a smaller kernel, and a faster computer, because you will only have support compiled for your computer. You should really get to know about your hardware before trying to recompile a kernel, though.