In my low-ish elo (silver to gold), I've been in too many games where the other team didn't have any smokes but were still running my team over on our defense side.

This happens because teams without smokes generally have more duelists or initiators, which mean they have even more entry power. So if your team commits really hard to holding site, the entrying team has the util advantage to storm site and get some picks, likely putting your team at a man disadvantage (2v5, 3v5, etc).

However, if you just play back, let them waste all their util on entrying and allow them to plant, they simply can't hold site as well. Not only because they just used up all their util on entrying, but also because they don't have smokes to block off angles.