Letting the clock run out.

Childish, isn't it?

I have been playing on Chess.com since 2010 and lately I have noticed a trend. I play mostly 15 min plus 10 second games. After the first 10 moves the opponent runs the clock down to 1 or 2 mins left before they really start playing, and then they move quickly to add 10 secs back to their clock. What is the strategy here? Are they hoping they will catch me off guard and win on time? I started really noticing this happening about 6 months ago and it happens at least 1 in 3 games I play on here.
Well said.