I don’t really believe there’s any real “advantage” in using asserts during a contest, at least, using asserts will not make your solutions better from the algorithmic point of view…
Usually, testers always use asserts when writing their solutions (which are written during the testing phase of the contest, done on the “backstage”, if you want to put it that way) because they need to make sure that the input files are well formatted and respect the given constrains. This is done mostly for two reasons:
It ensures that the test data is formatted and consistent with the constrains given on the problem statement;
It gives the problem setter’s the possibility of fixing any mistakes, if there are any;
This way, it is 100% checked that the problem is well-written and that the test data is well formatted.
As this is done during the testing phase, competitors usually don’t need to use asserts when writing code
Hope this was helpful.