Every solution that gains advantage comes a some cost.
If you have 100 or 1,000 eValid browser users running, then, yes, there are some downsides.
For example, if your application involves writing to a local file, then you have to parameterize the name of the file so that now two of the parallel-executing browsers will step on any others' results.
Or, if your application needs to validate something on a screen, then you have to use the lock/unlock to prevent two (or more) eValid instances from interacting badly by trying to read the same screen. (Remember, in Windows there is only one screen.)
In general we try to make applications that are going to be tested in parallel "desktop safe" so that they CAN run in multiple numbers in parallel.
eValid Loading Support Team