Do you continue to train for mass or try to lean up? Seems like a simple question with an easy answer, right? Sure, if you actually compete, but what if you're one of the many -- the majority -- who do not compete or haven't competed in years? When do you decide to go into a cutting phase?
Bodybuilding, whether you do it competitively or only as a hobby, is an extreme lifestyle. In order to be successful you have to be. Think about. You really need to train at least 3-4 days per week and monitor your diet all day long -- everyday! If you're trying to gain size, you'll need to eat 4-7 times per day and your protein intakes is probably at least twice that of an average American. If it's "offseason" you can eat as many carbs as you want. Your only limit is how big your gut gets. And that's where the dilemma comes in.
Extreme eating is done to gain size even to the point of force feeding in order to pack in enough calories so the muscles can grow. Flood those fibers with nutrients all day long so there isn't even the slightest chance to veer from an anabolic state due to calorie restriction. (Some guys even get up in the middle of the night just to eat!) You get used to trying to never be hungry and eating at specific times during the day rather than wating a couple hours for you stomach to empty and hunger returns.
Then one day you decide to rip up for (fill in the blank). You cut back on the carbs and keep the protein high and eat at least 6 times a day to "keep the furnace stoked" so you can burn fat at an incredible rate that will shock all your friends who use Jenny Craig or WeightWatchers. But guess what? Since you're used to force feeding every two hours you feel like you're starving and want to eat everything in sight. Food and the burning hunger is all you think about.
If you decide to rip up, go for it and don't hold back. Don't worry about losing a little size in the process.
If you want to gain mass, don't get sloppy fat.
Train hard and enjoy the journey! You are blessed, fortunate and lucky to be on it.