Konqueror, is used on a wide variety of computers by a wide variety of users. Under the category of performance, this dialog allows each user to adjust options which may make the computer that Konqueror is installed on feel more responsive.
The subsection labeled Preloading makes a tradeoff between memory and performance.
Preloading refers to loading an instance of Konqueror into memory before a user asks to start Konqueror. The positive effect of this is that when a user asks to load Konqueror the window appears instantly because most of the application has been preloaded. The negative effect is that this instance of Konqueror uses memory that could be used by other programs. By default, when a user closes Konqueror, the instance is not closed. This means that the next time a user wants Konqueror loaded, it is nearly instantaneous again.
The final check box labeled Always try to have at least one preloaded instance signals that you always want to have one preloaded, but not used, instance of Konqueror available. This option will actually decrease performance on some machines (especially those with limited physical memory).