Felix. One time Felix came to camp about 30 pounds lighter and had a terrible year. He didn't get back to himself until he got his dad body back. Big Meaty 6'4'' pitchers throw harder and are more durable. 250lb clydesdale Roger Clemens and Curt Shilling types are the stuff that championships are made of. The extra fat helps them regenerate faster or something. Note that BR lists Clemens and Shilling as 205 lbs each. BR lies at all times about players' weight. Those guys would have become ravenous and ate batters if they were 205 lbs.
220-250 is a sweet spot for pitchers. They get one level of suspicion for every 15 lb variance from this window. But, if you throw 98 for 200 innings all is forgiven.
Otherwise, what Matt said. Being 50 lbs overweight makes you a clogger on the basepaths, an inept fielder and sets you up for rapid decline in your early thirties and increases your injury risk. Think Bucky Jacobsen. But, if you slug .800 all is forgiven. I don't know about giving a 30 year old position player over 230 lbs a flaghship contract though. Prince Fielder is a little too recent.