It's a personal preference thing. Personally, I wear them on hard training rides, group rides, or races (where I would be gripping the bar tighter, sweating more, or have a higher risk of crashing) but don't wear them on recovery rides. I have Lizardskin bar tape and find it plenty comfortable and tacky without gloves, but I've also crashed and put holes in my gloves so they also may help. There will be crashes where you are wearing gloves and they don't help or crashes where you aren't wearing gloves and your hands are perfectly ok.