Most riders will never have any negatives from owning them.
But, many years ago, I was riding with a guy who had the BIG crash bars on his XS500 (same tank and brakes as my RD350). He touched down the bar in a corner and it unloaded the back tire enough to make him crash.
After that, I thought that the term "crash bars" was appropriate.
On the plus side, he was relatively uninjured and the bike was still completely rideable (busted back turn signal)