Never hurts to have them on record. Stiffens the spine for later when it can count. They don’t want to waffle back and forth...so now they’re on record and less likely to change in the months ahead as a result. They also have to run on this vote, another good thing, the Dems have to run on their vote but so do the R’s. Another reason they can’t waffle now.
This will only come up in the Senate when Harry Reid is back in the minority. He won’t bring it to the floor for exactly the reasons pointed out in this thread.
The issue, however, is costing them dearly anyway. Look to the recent polling in FL, where Mack is breaking big over Nelson. And that’s just one example.