Although the path of muscle building begins at a definite point in time, it rarely has an end. Once a person sets out on their journey to get in shape, they're hooked so to speak. Regular resistance training and aerobic exercise combine for an excellent habit that's tough to break. That said, and although it clearly has its advantages, there are hardships along with some downsides to making muscle building a part of your lifestyle.
There's an argument to be made about whether a lifter needs to train with increasingly heavy weights in order to consistently grow in terms of muscular development. And while it may, in fact, be true, one certainty is that this becomes less significant as increases in rest periods, both pre and post-workout, are made. The same could be said about a few other factors, such as simply eating more.
But similar to eating excessively (even if it consists of eating the right foods) or over-sleeping for that matter — consistently training with heavier weights becomes futile beyond a certain point. The key to consistent growth is continually improving on all areas associated with muscle building. This is, of course, if a balanced lifestyle (meaning, one including areas outside of physical results) is important to you... which, in my personal opinion, should be.
So what bad could possibly come out of choosing the muscle building path?
Tension
While it might not completely tarnish a relationship, tensions arise when a person decides to make muscle building a priority in their life. Family, friends, colleagues, and other peers often have a difficult time understanding the sacrifices (the steps, essentially) needed to build muscle. Working a 9-to-5 job; normal. Attending a post-secondary school either part or full-time; normal. Training regularly and monitoring your diet 24/7; strange and/or irrational.
Oddly enough, individuals choosing this path may even encounter aggression from loved ones. At the very least, occasional frustration on the part of those closest to you will likely be the norm. The same could be said about any aspect of your life, but this usually happens at another level. The optimal solution, in this case, is to be assertive in your actions. If you identify with being muscular, then so be it (cue period). There's no need to go the other way or separate yourself from these people; they probably care very much about you, however, like most — hate what they don't, can't, or choose not to understand.
Obsession
We've already touched upon the concept of being addicted to training, or, for some, the feeling of being muscular in general. But let's briefly discuss what it could lead to.
There are worse habits than getting in shape and making it a priority in your life. That said, emphasizing on your body does detract from other, sometimes more important, facets of your being. While it's not for everyone, something I've personally found to be helpful is integrating this obsession of muscle building into those facets. It might sound counter-productive, as now everything would seem to be amplified (given the inclusion of what we're attempting to control), but it's really quite simple; we're spreading it out in a way that actually reinforces these other areas, basically helping them to mature as opposed to setting them up to work against one another.
Muscle building in and of itself (i.e, the regular workouts, the meticulously-followed nutritional regimen, etc) does assist with developing the discipline required to accomplish other great tasks & feats. It also offers the potential to improve one's posture (consequently and arguably improving their mood), mental focus, and so on. You can start a business around this passion — one that will allow you to directly or indirectly profit from it (justifying your high degree of involvement, whether it be for yourself or to appease others). You can become a bodybuilder or another type of strength sport athlete. It may provide the physical strength needed to help an aging or sick parent, sibling, spouse, or child.
Time
Regardless of how long or short-lived your muscle-building path will be, the weekly commitment to this endeavor is great. As little as 20 minutes and as much as 3 hours may be spent in the gym, often on a near-daily basis. If you're traveling to and from a local fitness center (as opposed to training at home or your workplace/school), that could take up a significant portion of your schedule as well. Is it worth your time? This depends on you and your life.
Whatever the obstacles may be on your muscle building journey, understand that, to an extent, this is who you are. If it's the case, you'll be doing yourself a favor by confronting them head-on. Maybe you're genetically predisposed to training with weights. Maybe becoming a fitness model is your calling card. Maybe it's for health/medical reasons. Maybe it's just something you enjoy — almost as a form of meditation or, dare I say, escapism from the harsh realities of this world. Despite it all, I don't think anyone would argue that, from an objective perspective, the benefits overwhelmingly outweigh the drawbacks.