I'm one of those people that really have a hard time getting up in the morning. That means that mornings are a terrible rush with no a second to spare. If you plan on cooking a meal in the slow cooker you have to plan for it and be organized.
To be organized for a slow cooker it means you have to have the food in the slow cooker before you go out in the morning. This in turn means you have to either do all the preparations the previous evening and simply put everything in the slow cooker in the morning before you switch it on. Or, the other option is you have to get up early in the morning to get the food going in the slow cooker.
Well, for me the first option does not work as I do not have a large enough fridge to store the whole lot overnight and there is no way I'm going to get myself out of bed earlier in the morning.
So, here enters my trusted pressure cooker. I can simply grab some meat in the morning and put it in the fridge to defrost. That only takes a second and them in the evening when I get home, I can have the food on the table in no time at all.
This then is why I say the most important difference between pressure cooker and slow cooker, to me, is the cooking time of a pressure cooker. There are many more, but this is the most important one for me.
Have a look at some of the other Difference Between Pressure Cooker And Slow Cooker.