Depends.
On the Dem aisle their list of witnesses have the potential to do damage--to themselves. Might be better for them not to testify.
On Alito's side it bolsters his case for confirmation to have strong character witnesses that include ABA (known to be Leftward tilt in past), as well as sitting Liberal and Conservative Judges. The Dems want an excuse to filibuster, delay or vote no. These Judges, particularly the Liberal Judges on the Circuit, damage their excuse considerably. If anything, it takes an already strong hand and encases it in steel to have their testimony included.
Thank you Soul for explaining - I am on a hit and miss kind of day.