Your roams basically depend on your evaluation of your adc.
If your bot lane is going to be 17 minutes of doing nothing but farming, which isn't stacking your Eyeball collections/Legend runes/getting you assist gold while the rest of the map is becoming a high kill-death game, then by all means, leave your lane. You're better off helping top eek off a win or mid, than letting the game snowball to a point where you're only 7k Gold while the other team (except bot) is already at 12-13k Gold, and by the time you encounter them, the game is already over.
If your bot is competent and making plays, keep an eye on local jungle ganks, and see if you have a clear ward path to reach there and the right geometries to help. If you do, take 30 seconds to help but ping your adc that you are leaving. They might as well come too, and attempt a 3v1 vs the invade. Don't chase beyond what can be realisticall consider a counter gank shutdown. Get your bot fed and rolling.
Your decisions should really be about you. If your lane is systematically keeping you 0/0/0 or worse, it's not working when top is a 12 kill lane and mid is a 10 kill lane and jungle on both sides has been about a 10 kill game combined. That means their lanes are advancing exponentially versus yours. If leaving bot can help those lanes even out and get you back into the resource game, do it. And sometimes, even ask your adc to come along and explain why. They may be sucking at controlling bot lane or at least a stalemate, but they very well may be what top needs to counter its counter, and suddenly line up 2-3 kills by moving in on Top.
1-2 Turret sacrifices aren't the end of the world as long as they aren't also accompanied by a drake at the same time. If you're roaming Drake times, you're probably going to have a higher chance of losing.