Each package offers its own unique strengths and weaknesses. As a whole, SAS, Stata, and SPSS form a set of tools that can be used for a wide variety of statistical analyses. With Stat/Transfer, it is very easy to convert data files from one package to another in just a matter of seconds or minutes.
Therefore, there can be quite an advantage switching from one analysis package to another depending on the nature of our problem. For example, if we are performing analysis using mixed models, we might choose SAS, but if we are doing logistic regression we might choose Stata. Moreover, if we are doing an analysis of variance, then we might choose SPSS.
If we are frequently performing statistical analysis, it is strongly recommended to consider making each one of these packages part of our toolkit for data analysis.