My answer to the question every time is, "YES"!
Many years ago, before I was an agent myself, my husband and I purchased a new home. We were very excited about our next move up in the housing market. The home was vacant when we started the negotiations. We closed within 30 days and everything we well. At the closing the previous owners handed over the keys to our new home. They asked if we were going to move in right away. We told them that we were leaving the next morning for two weeks to visit my husband's family up north. That afternoon, we picked up our kids and moved a couple of things in the house just so it would feel like it was really ours.
Returning from our vacation we went straight to our new home. As we walked in the door, I noticed a key on the kitchen counter. I didn't remember leaving that there... As we walked around, I discovered that the curtains in the two front bedrooms were missing. I was not broken hearted about this but it looked like the just pulled the hardware out of the wall! There were big holes in the sheetrock! As I went to adjust the fan, I realized the fan pulls were missing as well!
You guessed it! The owners had come into MY new home while we were away and took the curtains and the fan pulls along with some other minor things. Boy did I feel violated! Someone was in MY home without my permission while I was on vacation!
My next action was to call the locksmith. He came out and changed the locks all around the house. I later found out that two of the neighbors still had keys to my house. Hindsight being what it is...I gave them (the previous owners) permission to enter my home by telling them we were leaving the next day for a vacation. Learned my lesson there!
So yes, I always tell my buyers to schedule a locksmith to come out and change the locks. You never know who may have a key and who may not be afraid to use it!