Most options are clear (if not, feel free to let me know :-)).

Less obvious options are:

- Set fans to 100% on program exit

This option sets fan at full speed when closing SpeedFan
- Delta value for fan speeds

This is the amount by which SpeedFan will increase or reduce fan speed percentages when it is instructed to change fan speeds according to temperatures
- Enable DELL support (use this function only on DELL notebooks)

This option will try (when you will restart SpeedFan) to access hardware monitoring options available only on some DELL notebooks
- Debug mode

This option will output additional info while the program is running. This info will be useful when asking for support
- Let SpeedFan access sensors through

Most sensors are accessed through ISA or SMBus. ISA is available on every PC, even if there is no ISA SLOT. ISA is fast and if a sensor chip appears both on ISA and on SMBus (like most WINBONDs do), you should prefer ISA access. SMBus is slower, but several sensor are accessible only through it.
Please note that disabling ISA and/or SMBus won't avoid SpeedFan from probing those BUSes. SpeedFan will simply not use them after having found them.