Barely perceptible, I'd wager. The indexes will only grow (in comparison to current) when there are entries of length >64 (varchar isn't padded). But the "session" field is a longtext, so it isn't exactly a high-performing table as it is. (just looking at a D5 install, YMMV for D6+). But it's probably beside the point because:

 

^this! :)

-D