+[UIImage imageNamed:]
• Reads the file, uncompresses it, caches result
• Cached copy of data is kept even if the UIImage is deallocated
• Low memory condition causes cache to be purged.
• No direct control over when cache is purged.
• Use for small frequently drawn images.

+[UIImage imageWithContentsOfFile:]
• Just reads enough of file to determine if it can open the file.
• Reads and uncompresses the file each time it draws. Uses uncompressed size worth of memory only temporarily.
• Assigning a UIImage created this way to a UIImageView or as the contents of a CALayer also causes it to read and uncompress the file. The UIImageView or CALayer keep the expanded version.

Memory Usage (in MB) 8.6 MB image used with UIImageView

	imageNamed	imageWithContentsofFile
Initial	2.46	2.46
Load UIImage	11.12	2.51
Assign to UIImageView	11.09	11.09
Remove from UIImageView	11.12	2.51

Memory Usage (in MB) 8.6 MB image used with UIView subclass (stored in instance variable and drawn with drawinRect: )

	imageNamed	imageWithContentsofFile
Initial	2.73	2.73
Load UIImage	11.38	2.78
Assign to UIImageView	11.81	3.20
Remove from UIImageView	11.84	3.04

Спасибо за некоторые пояснения Андрею Копаневу :)

– Robert Clair