You're not good enough yet.
I actually mean that you're probably in your skill bracket, or so close to it, that when you choose to make one of those two choices, the risk of neglecting the other option IS apparent. Chances are, if you did this against much lower skilled opponents, it'd work out just fine, but for a whole mess of reasons outside of the strategy.
You leave lane but you're not followed by your opponent? Then they are probably shoving that tower and aiming for that tower bonus.
Your lane opponent is roaming but you can't/won't follow? You're hoping your team makes the difference and plays safe, assuming you pinged/warded.
Games always been about balance and play-calls. Some games you should roam, others you should farm, some both. You need to learn to read the situation and figure out which option is best.
I lean towards farm, but there are definitely times where roaming helps. Actually, in THIS season, I can roam, getting a successful gank, a tower with the bonus, and possibly a dragon.
Weigh your options. Weigh the costs. Weigh your opponents. Weigh the scuttle crab if it's cooperative.