So here's one to watch for. If the Tool Change retraction in the "Other" tab is set to retract AND you are using a Prime/purge and a wipe you can get a blob at the start of your tool path which you do not want! The tool retraction happens right before the "T" command, and the tool is parked, then a tool is picked up, purge/prime/wipe, then the gcode continues but starts with the reverse of the retraction which at this point is not what you want because you have material at the hotend ready to extrude. The hotend is over the previous layer and then extrudes the reverse of the Tool Retraction right on to your object. So... if you are using a purge/prime you probably want to set Tool Retraction Distance to 0.