No one likes to see too much fat anywhere. It is great when it lightly surrounds a New York strip steak, or slowly tenderizes a roast, but not in too many other places. It definitely does not belong in SQL transaction logs.
Unfortunately, some transaction logs get bigger and bigger, some by gigabytes a day, or even in hours. This is usually indicative of a problem.
The Altiris KB article entitled "Why is the SQL Transaction Log growing by Gigabytes Daily?" and found at https://kb.altiris.com/article.asp?article=35211&p=1
outlines one way that this can happen, and how to keep it from happening in the future.