In addition to breaking ties in the Senate (and usually presiding in the EC count), filling in for the president, 25th amendment, don’t forget protecting the space-time continuum 
http://www.cc.com/video-clips/p1jk76/futurama-action-rangers
Brian
It’s certainly going to inconvenience Harris, but I don’t think her having to be available for ties is going to significantly impact her ability to play a role in the Administration. Schumer has some latitude to schedule votes so that they can work around her schedule, the Senate takes plenty of recesses – I mean “district work periods” – when she’s free to do as she likes.
During the seven months when the Senate was tied in 2001, Dick Cheney only ended up casting two tie-breaking votes. Things have certainly gotten more partisan since then, but Schumer should have a pretty good sense of which votes he’s going to need Harris for in advance.