1:Caulking is not a required item unless there is a mold /black growth problem which requires caulking to resolve the problem

2:SDCPM recommends caulking for both cosmetic and preventative maintenance reasons.

3:Caulking can help prevent  water damage and future mold problems . Caulking around sinks, baths, toilets, and tubs will deteriorate with time creating
     that ugly black mold in the grout and leaks either in the unit or worse, into other units. The caulking and seam breakdown in this photo can cause leaking
     into a unit below.The worst relates to water or moisture intrusion usually found where there is plumbing. Caulking should be forced into cracks then 
      smoothed to provide a bond. 

4:Caulking is also recommended to reduce the costs of pest control , to fill gaps that pests can use to hide etc.