Crop Marks VS Trim Marks

Crop marks being used as live effects. Effect > Crop Marks

• Marks that are used to apply for marking where document trim marks are
• Crop marks should not be used on bleed corners

Trim Marks used around your artboard. Object > Trim Marks

• Where the document windows cuts off

• Crop marks do not replace trim marks created with the Marks & Bleed options in the Print dialog box. Create crop marks around an object In Illustrator, you can create editable trim/crop marks or create crop marks as live effects.'
• Always use crop marks where the trim is

Adding Crop Marks

SOURCE:
https://tinytutorials.wordpress.com/2011/02/20/adobe-illustrator-cs5-trim-marks-vs-crop-marks/