Back to 1998. Mac users loved Mac OS 8. Mac OS classic were a limited OS; without memory protection, any application would crash the system.
People likd to install extensions on Mac OS classic to overcome some limitations back then. However, due memory lacks or so, the system would turn unstable in ocasions.
On this topic, a Mac Apologist would say that "Apple build the system simplier and extension developers don't care about stability" instead "Apple should put memory protection on mac os so developer get a breath".
Now talking about the new times: if you close mail and safari, you have nearly 50MB max free of memory to run another application. since iphone os don't have any smart methods (garbage collection) to avoid losts pointers to memory allocations, then any application from app store or from cydia can leak and then, put your iphone on low memory conditions..
So that sentence "I don't care about low memory conditions, because Apple signed apps are good" is simply not acurate, since Apple do not have exaustive testing (even with their software).
So, if you getting a jailbreak, do a test-drive with the apps you may need first. Its better to control the material than the material controlling you.