SoundFont tab configures SoundFont support. It works only with SoundFont-compatible devices (read: SBLive).
Autoload SF2 files feature allows you to add separate SF2 file to every MIDI file. For an example, it allows you to play correctly all files from SoundFont SDK.
Use custom bank for all MIDI files loads selected bank on playback start and unloads it on stop.
Fix missing drum kits remaps loaded drum kits to ensure that all drum track are played (even if incorrectly).
Disable SoundFont supprt prevents SoundFont DLLs from being loaded (saves memory); recommended if you don't use SoundFont stuff at all.
A few notes about SF2 file loading. The plug-in loads only used instruments to memory; it doesn't load whole SF2 file. It allows you to use those >100meg SF2 files most of time. For an example, you can clear any statically loaded banks, reduce allocated memory (eg. to 4 megs) and specify some bigger bank (eg. 8-meg one) in the plug-in config.