Two comments:

1. If you're going to store dates in a varchar, at least store it in YYYYMMDD format.

2. Implicit conversions can also cause poor performing queries. Say you have a six-digit char column, zero-prefilled so that you have data like "001843". If you search for 1843, it will find the match, but it will also convert all of that column to an int. Even if you have an index on that column, it now won't be used.