stl has pretty much to check, but when everything is configured, several option-checks can be disabled (per game) to speed up the actual game start process. Here are some examples which improve the start notably (all settings can be configured in the Settings Menu)

• set WAITEDITOR to 0 Wait requester
• set CHECKCATEGORIES to 0 if the Game has no Steam Category Tweak anyway
• set SAVESETSIZE to 0 when all windows have their optimal Gui Window Size
• (IMHO) games start much faster when stl is configured as Steam Compatibility Tool instead of Launch Option. The reason is simply that the Steam Linux Runtime isn't loaded when using a Steam Compatibility Tool.