Elimination of bad multitasking, as one of the main features of Critical Chain Project Management (CCPM), implies that there is also a good level of multitasking that can be retained in such environment. Although there have been attempts to define good and bad multitasking, the boundary between them is not yet lucid in practical terms. The present study intends to clarify this boundary for multi-project environments with ten different rates of resource availability using Monte Carlo simulations of randomly generated project data. The conclusions drawn from results of simulations of ten portfolios with similar size, variability and complexity levels, each containing four projects, show that while no level of multitasking is good for portfolios with resource availability rates of 170% of all resource requirements or higher, for lower rates, a good multitasking of up to two tasks at the same time can be distinguished from multitasking of 3 tasks and more as bad multitasking. This is a significant contribution to the theory of CCPM because of its implications for the roadrunner mentality recommended by CCPM and the fact that for the first time a boundary is suggested for determination of good and bad multitasking in multi-project environments.