Lagging is a skill. It is variable just like any other skill in the game. Nobody strikes it exactly the same every time for any shot including the lag. Then you have early match jitters etc etc. Everyone comes to the table for the lag in a slightly different headspace so there will always be variation from one lag to another. It's as fine a way as any to start a match and there's nothing wrong with it.
Side note: I recently brought it to my league operators attention that some players are deliberately stalling to gain an advantage. Waiting until the opponents ball is almost stopped to strike theirs. Has happened to me twice. First time I almost froze it so it didn't matter, second time though I got it to maybe the middle of the rack depth wise and the guy easily beat me. I didn't say anything at the time because I don't like to argue during matches unless it's a BIG deal cuz all it does is get in MY head.