well this really depends on your cells. But having a NaCl solution is in that sense better than having pure destilled water. I wouldn't leave them to long in this solution though. After some hours they might not be the healthiest anymore. Better are typical cell culturing solutions (e.g. DMEM) etc. But for transient maintainance it should be alright. I hope that helped you a bit.
I shall prefer using buffered compatible solute (such as proline, glycinebetaine, mannitol or sucrose) or high molarity buffer (for instance instead of using 50 or 100 mM you can use 200 or 250 mM phosphate or MES or Tricine buffer). They generally do not interfere with most of the assays. NaCl can have a negative impact on your assays.