Many people do not realize this, but with all versions of MultiFinder, the System Heap can actually grow even after start up time, easing INIT memory conflicts. If an INIT asks for more memory than is available, the System Heap will automagically get bigger. However there are two bad things about this: 1) the System Heap will grow, but never shrink again and 2) Several well respected Macintosh programmers have stated that they’ve seen cases where MultiFinder CANNOT expand the System Heap automatically, and die in the process. This is apparently extremely rare however.
This makes claims of "you’ve got to increase your System Heap" even less powerful, because the system will increase it for you if need be.
System 7 changes the game entirely, the System Heap can grow and shrink at will to accommodate requests for memory, eliminating many INIT memory problems entirely. However System 7 threw INIT writers several other curves, so you’ll most likely need to upgrade your favorite INITs for use under System 7.0. You shouldn’t have to increase your System Heap manually for System 7.0, but you never know… an extra 20K or so never hurt anyone.