including template files in single file

Hi,

I have many stylesheets in the system. and they all use the same menu =
bars, toolbars, common functionality basically.. So what I do in each =
major stylesheet is that I include the common operations stylesheets, =
such as menu or toolbar. In doing this I minimize the change problems =
when I make change to the menu say..

Is this a fairly common practice and what effect is on performance, bcoz =
the compiler will load multiple files from the filesystem while =
generating output.

Also, in my case is "include" or "import" recommended.

Please let me know.

Thanks.