Most often it's going to be a nighttime raid. The problem is that they lump marijuana in with violent crime. If you're going to be selling heroin or coke, you have to have connections to other countries where they can get away with growing fields of the stuff. I don't know much about the process of making either drug, but I doubt you can grow a significant amount of poppies or coca plants in your basement and still make a profit. Also, I've met probably 100 people who've admitted to smoking pot, but only one person who tried cocaine (took a hit of crack) and one heroine user who got it while he was in jail for a non-drug related charge. How does one get those international connections? Usually it's by being a gang member, and gangs make things get violent quick. They kill informants, rival gang members, cops and anyone else who gets in their way because it's the only card they have to play. Unfortunately, all drug dealers get lumped into that camp and the cops take precautions.
Pot, on the other hand, is popular and easy to get seeds for. You can get seeds online, or you can grow bagseed. Even the worst strains of schwag grown hydroponically can yield some pretty good nug if the grower knows their stuff. This means that your average entrepreneur with a few connections in the world of dealing, can make themselves a tidy profit. They're rarely violent and often intelligent people who've found an easy way to make money in hard times. Smart growers don't own guns because they know it adds time if they do get caught. They don't resist arrest like some moron from the ghetto and they politely invoke their fifth amendment rights while they ask for their lawyer politely. They NEVER try to agitate the police in any way. Sometimes these nice people are raided at gunpoint and treated like scum.
Are some pot dealers vicious thugs? Yep, some sure are. Therefore, the cops take caution most of the time and raid when you're not expecting it. The risk is just too high. Either way, the safest thing to do is have a game plan for being raided. Don't own guns, period. Don't have a big vicious attack dog unless you want it to get shot in the head. Don't be a dumbass and try to fight the cops; that's what court is for.